
Class SSio--^ 
Book. ?■ ■ •• 



US2 



Copyright N° 



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COPYRIGHT DEPOSJT. 



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i 



Ube IRural Science Series 

Edited by L. H. BAILEY 



PLANT-BREEDING 



El)e Eural Science Series 

The Soil. King. 

The Spraying of Plants. Lodeman. 

Milk AND ITS Products, Wing. Enlarged and Revised. 

The Fertility of the Land. Boberts. 

The Principles of Fruit-growing. Bailey. '20th 

Edition., Bevised. 
Bush-fruits. Card. 
Fertilizers. Voorhees. 
The Principles of Agriculture. Bailey. 15th Edition,, 

Bevised. 
Irrigation and Drainage. King. 
The Farmstead. Boberts. 
Rural Wealth and Welfare. Fairchild. 
The Principles of Vegetable-gardening. Bailey. 
Farm Poultry. Watson. Enlarged and Bevised. 
The Feeding of Animals. Jordan. 
The Farmer's Business Handbook. Boberts. 
The Diseases of Animals. Mayo. 
The Horse. Boberts. 
How to Choose a Farm. Hunt. 
Forage Crops. Voorhees. 

Bacteria in Relation to Country Life. Lipman. 
The Nursery-book. Bailey. 
Plant-breeding. Bailey and Gilbert. Bevised. 
The Forcing-book. Bailey. 
The Pruning-book. Bailey. 

Fruit-growing in Arid Regions. Paddock and Whipple. 
Rural Hygiene. Ogden. 
Dry-farming. Widtsoe. 
Law for the American Farmer. Green. 
Farm Boys and Girls. McKeever. 
The Training and Breaking of Horses. Harper. 
Sheep-farming in North America. Craig. 
Cooperation in Agriculture. Powell. 
The Farm Woodlot. Cheyney and Wentling. 
Household Insects. Herrick. 



PLANT-BREEDING 




^PAILEY 



NEW EDITION REVISED BY 

ARTHUR W. GILBERT, Ph.D. 

• 

PROFESSOR OF PLANT-BREEDING IN THE NEW YORK 

STATE COLLEGE OF AGRICULTURE AT 

CORNELL UNIVERSITY 



THE MACMILLAN COMPANY 
1915 

All rights reserved 



^\ 



Copyright, 1S95, 1906, 
By L. H. bailey. 



Set up and electrotyped. Published December, 1895. Reprinted 
April, 1896; August, October, 1897; March, 1902; March, 1904. 

Fourth edition, with additions, April, 1906: April, 1907; July, 
1908; August, 1910; February, 1912; October, 1913. 



New Revised Edition, Entirely Reset. 

Copyright, 1915, 
By the MACMILLAN COMPANY. 



Set up and electrotyped. Published February, 1915. 



J. 8. Cushing Co. — Berwick & Smith Co., 
Norwood, Mass., U.S.A. 



FEB II 1915 

©CI,A'J9360il 



HISTORY 

This book had its beginning in a lecture that I gave 
twenty-three years ago (December 1, 1891) before the Mas- 
sachusetts State Board of Agriculture, in Boston, on " Cross- 
Breeding and Hybridizing"; and this lecture, in turn, was 
the outgrowth of one given in 1885 and soon afterwards 
published. Under the same title, but with a bibliography 
added, the Boston lecture was published as a pamphlet in 
1892, and placed on sale, by the Rural Publishing Company 
of New York, as one of the Rural Library Series. It com- 
prised forty-four pages, and sold for 40 cents. In the sum- 
mer of 1895, I gave two addresses on variation and the 
origination of domestic varieties of plants under the auspices 
of the American Society for the Extension of University 
Teaching at the University of Pennsylvania. In the mean- 
time, I had been teaching the subject to my classes in 
horticulture in Cornell University. In the latter part of 
1895, I put together these materials in book form, and hav- 
ing no short descriptive title I used the word or compound 
''Plant-Breeding." Of this work, the Massachusetts lec- 
ture comprised Chapter II, and the Philadelphia lectures 
Chapters I and III. The bibliography was not included. 
Chapter IV comprised ''Borrowed opinions" from the 
writings of Verlot, Carriere, and Focke. .Carriere's work 
on "Production et Fixation des Varietes dans les Vege- 
taux" had been translated, with a view to publication, as 
early as 1886. The book, " Plant-Breeding," was translated 



vi History 

into the French by J. M. and E. Harraca, and published in 
Paris in 1901 as " La Production des Plantes." 

Having been thrice reprinted, the second edition was 
issued in 1902, although, through an inadvertence, it was 
not so marked on the title-page. Few text-changes were 
made, but the bibliography was included. 

Early in 1904 the third edition was issued. The bibli- 
ography was extended, and some changes were made in the 
text; but the principal departure was a new Chapter IV, 
from which the old '- Borrowed opinions " were omitted, 
and " Recent opinions " were substituted, comprising a dis- 
cussion of the work of de Vries, Mendel, and others, and 
a statement of the current tendencies of American plant- 
breeding practice. " In the eight years since this book was 
sent to the printer," it was stated in the preface to the third 
edition, ''there have been great changes in our attitude 
toward most of the fundamental questions that are dis- 
cussed in its pages. In fact, these years may be said to 
have marked a transition between two habits of thought in 
respect to the means of the evolution of plants, — from the 
points of view held by Darwin and the older writers to 
those arising from definite experimental studies in species 
and varieties. We have not given up the old nor wholly 
accepted the new, but it is certain that our outlook is shift- 
ing. So far as practical plant-breeding is involved, the 
changing attitude is concerned chiefly with discussions of 
the nature of varieties and the nature of hybridization." 
It was declared that " the time cannot be far distant when 
the subject of plant-breeding will be rewritten from a new 
point of view." 

In 1906, the fourth edition appeared, with a new chapter 
on " Current plant-breeding practice " ; and the book had 



History vii 

grown from the 293 pages of the original edition to 483 
pages. This edition was translated into the Japanese by 
D. Karashima, and published in 1907. 

We now come to the present edition. The book has been 
made over by Dr. Gilbert, who has rewritten some of it 
and who has added all the new material, and in whose 
hands I have been glad to place it. My work in this 
edition has been only editorial. A considerable part of the 
old work has been preserved, whether wisely or not will 
be the occasion for different opinions. It has seemed to be 
desirable to retain something of a former point of view 
while at the same time expressing the applications of the 
work in the method and the language of the day. Con- 
siderable use has been made of the work of others, as is 
apparent in the pages. The Open Court Publishing Com- 
pany has loaned illustrations from the important work of 
de Vries, and pictures have been taken from the Yearbooks 
of the United States Department of Agriculture. All these 
aids we are glad to acknowledge. 

These new investigations have taken us far from the 
point of view of Darwin, in which the original editions of 
the book were founded. I doubt whether the students 
receiving their instruction to-day, Avith all their abounding 
facilities and opportunities, have any such feeling for a 
master-spirit as we had in those days when the studies of 
Darwin had given a new meaning to nature, when there 
were still a few naturalists left, and when the glow of his 
writings was warm in every person's work. To one coming 
out of a plant-growing relationship, the masterful works of 
Darwin had introduced order, and the forms of cultivated 
plants had been made worthy of serious study. This inter- 
est was further stimulated by the writings of Wallace and 



viii History 

others. All these writings were fascinating to read. How 
to produce new forms of vegetation seized some of us with 
irresistible power. The literature has now become complex 
and difficult, with considerable gain, no doubt, in a closer 
acquaintance with the subject, and a nearer approach to the 
ultimate truth ; but the charm of the simple literature is 
largely buried, and I fear that much of our interest is now 
expressed in the discussion of methods and in disputing 
about the reasons. Yet we are accumulating knowledge, 
and after a time we shall come back to clarity and to a 
simplicity that the layman can use. 

L. H. BAILEY. 

Ithaca, N. Y., 

December 1, 1914. 



TABLE OF CONTENTS 



CHAPTER I 

PAGES 

The Fact and Philosophy of Variation . . . 1-13 

The fact of individuality, 2 — variation and adapta- 
tion, 7 — species-formation, 8— conception of unit char- 
acters, 9 — differences between plants and animals with 
regard to general association of parts and their methods 
of reproduction, 10 — bud-variation and bud-varieties, 11. 

chaptp:r II 

The Causes of Individual Differences .... 13-33 
Fortuitous variation, 14 — action of natural selection 
on variation, 14 — sex as a factor in the variation of 
plants, 15 — physical environment and variation, 16 — 
do external influences produce permanent effects in 
plants, 17 — natal and post-natal variations, 18 — con- 
ception of biotypes, 19 — variation in food supply, 20 
— variation in climate, 22 — food supply in different 
branches, 23 — what cultivation is, 24 — variation in cli- 
mate, 25 — man's control over climate as a means of 
making plants vary, 27 — change of seed, 28 — bud- 
variation, 29 — struggle for life a cause of variation, 30. 

CHAPTER III 

The Choice and Fixation of Variations . . . 34-40 
What is a variety, 35 — adaptation in nature, 37 — 
artificial selection, 37— bud selection, 39 — variation 
and selection not entirely within man's control, 39. 

ix 



X Table of Contents 

CHAPTER IV 

PAGES 

The Measurement of Variation 41-51 

The science of biometry, 41 — type, 43 — biometrical 
expression of variability, 43 — mode, 44 — modal coeffi- 
cient, 45 — mean, 45 — use of mean, 46 — mathematical 
expression of variability, 47 — average deviation, 47 — 
standard deviation, 48 — coefficient of variability, 49 — 
probable error, 50 — use of statistical methods, 51. 

CHAPTER V 

Mutations 52-91 

Evolutionary theories of Darwin and de Vries, 52 — 
differences between fluctuating variations and mutations, 
54 — history of mutation, 55 — history of the appear- 
ance of double flowers, 56 — de Vries' experiment with 
Oenotheras, 59 — analytical table of seedlings (after de 
Vries), 68 — how the mutants were produced in the gar- 
den, 71 — mutating strains of O. Lamarkiana^ 72 — de 
Vries' laws of mutability of the evening-primroses, 72 — 
frequency of occurrence of mutations, 79 — spontaneous 
occurrence of new elementary species in the wild state, 
80 — spontaneous occurrence of new elementary species 
and varieties under cultivation, 80 — experimental study 
of the origin of nuitations, 84 — experiments in the pro- 
duction of double flowers, 86 — what do new characters 
come from, 90 — can mutations be produced artificially, 
90 — economic significance of mutations, 90. 

CHAPTER VI 

The Philosophy of the Crossing of Plants, considered 
IN Reference to their Improvement under 
Cultivation 92-148 

The struggle for life, 92 — survival of the most fit, 93 
— flexibility as an aid to survival, 93 — causes of varia- 
bility, 94 — origin and function of sex, 95 — effects of 



Table of Contents xi 



crossing on the species, 97 — the limits of crossing, 97 

— swamping effects of inter-crossing, 98 — what deter- 
mines tlie limits of crossing, 98 — the limits of crossing 
tend to preserve the identity of spocies, 99 — the refusal 
to cross, the result of natural selection, 100 — for the 
production of useful hybrids, do not have the parents 
too diverse, 101 — function of the cross, 101 — rarity of 
natural hybrids, 102 — change of seed and crossing, 103 

— results from change of stock, 105 — crossing from 
standpoint of plant improvement, 108 — understanding 
of terms, 108 — history of plant hybrids, 110 — what 
plants can be hybridized, 111 — vigor as a result of 
crossing, 112 — Darwin's experiments with morning- 
glories, 114 — Darwin's results with other plants, 115 — 
increased vigor in other crosses, 115 — three factors, 117 

— the outright production of new varieties, 118 — how 
to overcome antipathy to crossing, 121 — variability of 
hybrids, 122 — characteristics of crosses, 123 — difficul- 
ties in making successful crosses, 125 — hybridization 
and asexual propagation, 125 — in-breeding, 127 — expe- 
rience with egg-plants and squashes, 128 — influence of 
sex on hybrids, 138 — uncertainties of pollination, 140 

— graft hybrids, 142 — the case of Cytisus Adami, 142 

— Winkler's SoJanum graft-hybrids, 146 — are these 
real graft-hybrids, 147. 

CHAPTER VII 

Heredity 149-208 

Heredity studied collectively, 149 — the coefficient of 
heredity, 152 — notation, 153 — conception of unit char- 
acters, 154 — knowledge of heredity has come through 
experimental breeding, 154 — rediscovery of Mendel's 
work by de Vries and others, 155 — Mendel's experi- 
ments, 157 — explanation of mendelian results, 166 — 
explanation of diagram, 171 — Mendel's results with the 
offspring of hybrids in which several differentiating char- 



xu 



Table of Contents 



actei-s are associated. 171 — Mendel's law of inheritance 
of unit characters (table), 175 — results in F-2 with com- 
plete dominance in every character-pair (table 1), 176 — 
results involving three pairs of characters (trihybrid), 
177 — incomplete dominance, 179 — presence and ab- 
sence hypothesis. 181 — examples of mendelian inherit- 
ance due to the presence and absence of a single unit, 
181 — mendelian inheritance of color, 185 — white flowers 
in F-2 from red x cream, 187 — the ratio 9:3:4, 188 — 
colored forms from white x white and the 9 : 7 ratio, 
188 — Emerson's experiments with beans, 189 — absence 
factors. 192 — mutations resulting from mendelian segre- 
gation and recombination, 193 — mutations which men- 
delize are constant, 193 — mendelism in wheat, 194 — 
mendelism sunmiarized, 200 — application to plant- 
breeding, 202 — the probable limits of mendelism in the 
production of new varieties, 204 — conclusion, 208. 

CHAPTER VIII 

How Domestic Varieties Originate .... 

Indeterminate varieties, 209 — plant-breeding, 212 — 
plant-breeding by selection, 218 — rules for breeding 
plants, 222 — specific examples. 253 — the dewbeiTy and 
blackberry. 253 — the apple, 255 — beans, 260 — cannas, 
265 — thecabbage family, 267 — the chrysanthemum, 267. 



209-269 



CHAPTER IX 

PoLLixATiox : OR How TO Cross Plants .... 270-293 
The structure of the flower, 270 — manipulating the 
flowers, 281. 

CHAPTER X 

The Forward Movement in Plant-Breeding . . . 294-323 

Systematic improvement of plants, 295 — the plant- 
breeder should aim toward definite ideals, 297 — plant 



Table of Contents xiii 

PAGES 

improvement a serious business, 298 — the results of 
plant-breeding effort, 299 — state plant-breeding associ- 
ations, 300 — other plant-breeding associations. 304 — 
commercial breeding agencies, 308 — work of the council 
of grain exchanges. 310 — United States Department of • 

Agriculture and state experiment stations, 310 — work 
of the state agricultural experiment stations, 314 — in- 
struction in plant-breeding in the United States, 321 — 
Luther Burbank, 321. 

APPEXDIX A 
Glossary of Technical Plant-breedixg Terms , . 325-327 

APPEXDIX B 
Plant- BREEDING Books ....... 328-331 

APPEXDIX C 

List of Periodicals containing Breeding Literature 332-334 

APPEXDIX D 
Bibliography 335-393 

APPEXDIX E 

Laboratory Exercises 394-467 

Exercise 1 — Field study of variations by making an 
herbarium of variations 394-399 

Exercise 2 — The statistical study of type and 
variability 399-412 

Exercise 3 — Correlation ...... 412—420 

Exercise 4 — Statistical study of apples from different 
trees 420 

Exercise 5 — Statistical study of branches of different 
trees 420-423 



xiv Table of Contents 



Exercise 6 — Statistical study of the quantity of grapes 

from different grape vines 423 

Exercise 7 — Study of variation in pressed specimens 
of ragweed or some plant showing many different types 423 

Exercise 8 — Study of bud variation and reversions in 

ferns 423-424 

Exercise 9 — Study of the morphology of different 

kinds of flowers 424-426 

Exercise 10 — Technique of the cross-pollination of 

plants 426-428 

Exercise 11 — Embryological studies from slides show- 
ing cell division at different stages, chromosomes, pollen 
mother cells, development of the embryo sac, etc. . 428 

Exercise 12 — Study of pollen germination and 

fecundation . 428 

Exercise 13 — Practice in the cross-pollination of ap- 
ples, pears, peaches, plums, etc 429 

Exercise 14 — Studies of mendelian inheritance . 429-435 

Exercise 15 — A study of mendelian characters in 

timothy and oats 435-438 

Exercise 16 — Mendelian problems .... 438-445 
Exercise 17 — Ear-to-row test with corn . . . 445-447 

Exercise 18 — Corn judging 447-448 

Exercise 19 — Statistical study of ears of corn . . 448-449 
Exercise 20 — Study of correlations of characters in 

corn 449-450 

Exercise 21 — Corn selection — laboratory study . 450-452 
Exercise 22 — A study in potato selection . . . 452-457 
Exercise 23 — Study of citrus hybrids . . . 457-458 

Exercise 24 — Study of the results of the plant-to-row 
tests of wheat, oats, cabbage, onions, or any crop where 
data are available ........ 458 

Exercise 25 — Studies of origin of varieties — corn, 
wheat, apples, plums, grapes, etc. .... 458 

Exercise 26 — Field trip to experimental grounds . 458-459 
Exercise 27 — Working plans for practical breeding 
experiments 459 



LIST OF ILLUSTRATIONS 



PIGTTRE PAGE 

1. Variation in heads of timothy ...... 3 

2. Two seedling timothy plants, growing side by side, showing 

a common kind and degree of difference ... 4 

3. A productive timothy plant 5 

4. A timothy plant that runs much to seed .... 6 

5. A timothy plant that runs almost wholly to leaf ... 7 

6. Couch or quack grass, showing means of asexual propaga- 

tion by underground root stalks 13 

7. Orange hawk weed . 32 

8. A frequency curve illustrating the distribution of the height 

of the pea plants ........ 42 

9. Variations in statures of (Enothera nanella^ a mutant, and 

CEnothera Lamarkiana, its parent . . . . .53 

10. Variations in the amount of sugar in 40,000 beets . . 54 

11. Ghelidonium majus 55 

12. Chelidonium Jaciniatum . 56 

13. Anemone coronaria, single-flowered form . . . . 57 

14. Anemone coronaria, semi-double-flowered form ... 57 

15. Anemone coronaria var. Jlorepleno ..... 58 

16. Hugo de Vries .59 

17. CEnothera Lamarkiana and (Enothera nanelJa in bloom . 60 

18. CEnothera Lamarkiana. Curve exhibiting variations in the 

length of fruits of 568 plants 61 

] 9. CEnothera lata — CEnothera Lamarkiana — CEnothera nanella 63 

20. J., spike with almost ripe fruits of CEnothera gigas, a mutant 

species; B, the same of CEnothera I^amarkiana, its 

parent form 66 

21. The cage in Professor de Vries' experiment garden, showing 

corn and various species of CEnothera .... 70 

XV 



XVI 



List of Illustrations 



22. 
23. 
24. 
25. 

26. 

27. 
28. 
29. 

30. 



31. 

32 
33. 

34. 
35. 
36. 

37. 
38. 
39. 
40. 
41. 
42. 
43. 
44. 
45. 

46. 
47. 

48. 
49. 
50. 
51. 



Cupid sweet pea (photo by Beal) . 

Linaria vulgaris — peloric flowers 

Linaria vulgaris peloria 

Antirrhinum majus .... 

Chrysanthemum segetum plenum . 

Chrysanthemum inodorum plenissim um 

Ancestral generations of Chrysanthemum segetum plenum 

A^ Chrysanthemum segetum; B, Chrysanthemum segetum 
grandiflorium (after purification) . . . . . 

Extreme variability in the shape of the leaves of hybrid pop- 
pies. Second generation from a cross between the Bride 
variety of the Opium poppy and the Oriental poppy 

Inbred corn plants, showing lessened vigor of growth 
(adapted from Yearbook) 

Hybrid walnut and parents . 

A hybrid walnut {Juglans calif ornica nigra).) reaching 
double the height of ordinary trees 

Variation in hybrid pineapples 

Variation in hybrid squashes 

Hybrid citrange and its parents, Poncirus (citrus) trifoliata 
and common sweet orange .... 

Hybrid tangelo and its parents, pomelo and tangerine 

Samson tangelo (adapted from Yearbook) . 

Citranges (hybrid of orange and Poncirus (citr^is) trifoliata) 

Teosinte and its hybrids with Indian corn 

Cytisus Adami ...... 

Cytisus Adami . . . . . 

Mendelism in maize 

Diagrammatic representation of Mendel's law 

Hybrid carnation between a single and a burster, showing 
intermediacy 

Fowls' combs 

Three generations of hybrid wheat 

Mendelism in tomatoes .... 

Pride of Georgia, a good short-staple cotton 

Select Jones improved cotton with uniform long staple 

Improving the tomato ...... 



PAGE 

78 
81 

82 
83 

86 
87 

88 

89 



96 

113 
117 

119 
123 
129 

132 
133 
134 
135 
137 
143 
144 
162 
170 

180 
184 
195 
203 
213 
214 
215 



List of Illustrations 



xvii 



FIGURE PAGE 

52. Crop averages in corn breeding for high and for low protein. 

Results of twelve generations. (111. Exp. Sta.) . . 216 

.53. Fruit of wild elderberry 217 

54. Fruit of a cultivated variety of the elderberry which ap- 

peared as a variation from the wild form . . .218 

55. Field of wilt-resistant watermelons, growing free from disease 

on infected land (from Yearbook) .... 219 

56. Disease resistance in cowpeas . . . . . . 220 

57. Improved types of lettuce and the varieties from which they 

were developed ........ 221 

58. Wild cabbage 240 

59. Curled kale 241 

60. Collard 242 

61. Brussels sprouts . 243 

62. Savoy cabbage , 244 

63. Cabbage shapes 245 

64. Swede turnip, kohl-rabi, and cauliflower .... 248 

65. Wild form of Chrysanthemum morifolium .... 249 

66. Wild form of Chrysanthemum indicum .... 250 

67. Pompon anemone type 251 

68. Single type 252 

69. Type of pompon chrysanthemum ...... 253 

70. Japanese anemone type ....... 256 

71. The small and regular anemone type ..... 257 

72. A pompon chrysanthemum ....... 258 

73. Type of Japanese incurved chrysanthemum . . . 259 

74. Japanese anemone chrysanthemum when fully expanded . 262 

75. New type with short stem ....... 263 

76. Incurved type 264 

77. Hairy type 267 

78. Japanese type 268 * 

79. Reflexed type 269 

80. Beimower 270 

81. Flower of white lily 271 

82. Flower of greenhouse cypripedium . . . . . 272 

83. Flower of night-blooming cereus ...... 273 

84. Flower of the shrubby hibiscus {Hibiscus syriacus) . . 274 



xviii List of Illustrations 

FIGCRK PAGE 

85. Bugbane {Cimicifuga racemosa) 275 

86. Blossom of flowering raspberry {Rulms ocloratus) . . 276 

87. Se^uash flowers of each sex ....... 277 

88. Flowers of clematis ( CZewia^is vzrgfjwmna) .... 278 

89. Tobacco flowers, showing the parts of the flower, a bud 

ready to be emasculated, and an emasculated subject . 282 

90. Zinnia flowers • 283 

91. Instruments used in pollinating flowers .... 284 

92. Ladle for pollinating house tomatoes ..... 285 

93. Bag for covering the flowers ...... 286 

94. Fuchsias, showing the stamens and pistils, and a bud ready 

to be emasculated .... 

95. Fuchsia flower emasculated 

96. Fuchsia flower tied up after emasculation 

97. Tomato and quince 

98. Pollinating kit 

99. Pollinating kit 

100. Main building of Seed Association, offices o 

pany (photo by Xewman) 

101. Gardens at Luther Burbank's 

102. Some of Burbank's frames and garden beds . . . 320 

103. Spineless and spine-bearing cacti at Burbank's . . . 322 

104. A specimen herbarium sheet, showing variations in the 

leaves of the mulberry ....... 395 

105. A specimen herbarium sheet, showing differences between 

two leaves of the horse radish ..... 396 

106. A specimen herbarium sheet, showing variations in leaves 

of the Persian lilac ....... 398 

107. A specimen herbarium sheet, showing variations in leaves 

of the blackberry 400 

108. A common form of ragweed 421 

109. Another form of ragweed ....... 422 

1 10. Demonstration of allelomorphism and of complete dominance 431 

111. Demonstration of presence and absence hypothesis and of 

intermediacy . 432 

112. Demonstration of the presence of an inhibitor factor . . 434 

113. Explanation of so-called " dominance and absence " . . 436 



. 287 

. 288 

. 289 

. 290 

. 291 

. 292 
f Swedish Com- 

. 307 

. 319 



XLbc IRural Science Series 

Edited by L. H. BAILEY 



PLANT-BREEDING 



PLANT-BREEDING 

CHAPTER I 

THE FACT AND PHILOSOPHY OF VARIATION 

There is no one fact connected with agriculture that 
more greatly interests all persons than the existence of 
numerous varieties of plants that seem to satisfy every need 
of the gardener. Whence came all this multitude of 
forms? What are the methods employed in securing 
them? Are they merely isolated facts or phenomena 
of gardening, or have they some relation to the broader 
phases of the evolution of the forms of life ? These are 
some of the questions that occur to every reflective 
mind when it contemplates an attractive garden, but 
they are questions that seem never to be answered. 
Whatever attempt the garden/sr may make at answer- 
ing them is either obscured by an effort to define what 
a variety is, or else it consists in simply reciting how a 
few given varieties came to be known. But there must 
be some method of arriving at a conception of the ways 
whereby the varieties of fruits and flowers and other culti- 
vated plants have originated. If there is no such method, 
then the origination of these varieties must follow no 
law, and the discussion of the whole subject is fruitless. 
But we have every confidence in the consecutive uniform- 



2 Plant-Breeding 

ity of the operations of nature, and it were strange if 
some underlying principle of the unfolding or progression 
of plant-life does not dominate the origin of the varied 
and innumerable varieties which, from time unknown, 
have responded to the touch of the cultivator. Let us 
first, therefore, make a broad survey of the subject in 
a philosophical spirit, and later, discuss the more specific 
instances of the origination of varieties. 

The fact of individuality. — There is universal difference 
in nature. No two Hving things are counterparts, for no 
two are born alike or into exactly the same conditions and 
experiences. Every living object has individuality; that 
is, there is something about it that enables the acute 
observer to distinguish it from all other objects, even of 
the same class or species. Every plant in a row of lettuce 
is different from every other plant, and the gardener, 
when transplanting them, selects out, almost uncon- 
sciously, some plants that please him and others that do 
not. Every apple tree in an orchard of a thousand 
Baldwins is unlike every other one, perhaps in size or 
shape, or possibly in the vigor of growth or the kind of 
fruit it bears. Persons who buy apples for export know 
that fruit from certain regions stands the shipments better 
than the same variety from other regions ; and if one were 
to go into the orchards where these apples are grown, he 
would find the owner still further refining the problem by 
talking about the merits of individual trees in his orchard. 
If one were to make the effort, he would find that it is 
possible to distinguish differences between every two 
spears of grass in a meadow, or every two heads of wheat 
in a grain-field. 



The Fact and Philosophy of Variation 3 

In timothy, one of the commonest of our grasses, a 
casual observer may find differences in the length, shape, 
and color of heads ; tendency of some plants to produce 
asexual leaves in the head; form of base of the head; 




m % 




i) '^. 



1 / Z -ij 4 6 6i 7 1 « 3; /Oj //,, /Z 




Fig. 1. — Variation in heads of timothy. 



length, mdth, and color of leaves ; erect or drooping 
character of the leaves ; susceptibility of the leaves and 
stems to rust ; period of blooming ; habit of growth of 
plant, — erect or decumbent ; few or many culms to the 
plant ; ability to recover after cutting ; quantity of seed 



Plant-Breeding 




The Fact and Philosophy of Variation 5 




Fig. 3. — A productive timothy plant. 



produced, and others (Figs. 1-5). Similar differences 
may be found in any group of plants if the group is suffi- 
ciently studied. 



Plant-Breeding 




Fig. 4. — A timothy plant that runs much to seed. 

Variation and adaptation. — All this is equivalent to 
saying that plants are infinitely variable. The ultimate 



The Fact aiid Philosophy of Variation 7 

causes of all this variation are beyond the purposes of the 
present discussion, but it must be evident, to the reflective 
mind, that these differences are a means of adapting 
the innumerable individuals to every little difference or 




Fig. 5. — A timothy plant that runs almost wholly to leaf. 



advantage in the environment in which they live. And 
if the result of variation is better adaption to the physical 
conditions of life, then the same forces must have been 
present in the circumstances which determined the birth 
of the individual. This change in environment may be 



8 Plant-Breeding 

the cause of much of the variation in plants, since differ- 
ences in plants were positively injurious if it were possible 
for the conditions of environment to be the same. 

Species-formation. — If no two plants are anywhere 
alike, then it is not strange if now and then some de- 
parture, more marked than common, is named and becomes 
a garden variety. We have been taught to feel that 
plants are essentially stable and inelastic, and that any 
departure from the type is an exception and calls for im- 
mediate explanation. The fact is, however, that plants 
are essentially unstable and plastic, and that variation 
between the individuals must everywhere be expected. 
This erroneous notion of the stability of organisms comes 
of our habit of studying what we call species. We set 
for ourselves a type of plant or animal, and group about it 
all those individuals that are more like this type than 
they are like any other, and this group we name a species. 

Nowadays, the species is regarded as nothing more than a 
convenient and arbitrary expression for classifying our 
knowledge of the forms of life, but the older naturahsts 
conceived that the species is the real entity or unit in 
nature, and we have not yet wholly outgrown the habit of 
mind which was born of that fallacy. Nature knows 
little about species ; she is concerned with the individual, 
the ultimate complete and working unit. This individual 
she molds and fits into the opportunities of environment, 
and each individual tends to become the more unlike its 
birthmates the more the environments of the various in- 
dividuals are unlike. 

We must consider, therefore, as a fundamental concep- 
tion to the discussion of the general subject before us, the 



The Fact and Philosophy of Variation 9 

importance of the individual plant, rather than the im- 
portance of the species ; for thereby we put ourselves as 
nearly as possible in sympathetic attitude with nature, and, 
resting upon the ultimate object of her concern, we are 
able to understand what may be conceived to be her motive 
in working out the problem of life. Recall the fact that 
the whole tendency of contemporary civihzation, in soci- 
ology and religion, is to deal with the individual person 
and not with the mass. The present-day method of study- 
ing the evolution of plants and animals is essentially an- 
alytical. As the chemist attempts to discover the smallest 
units from which the substances of nature have been built 
up, so the student of biology and evolution is seeking for 
the smallest heritable units of which plants and animals 
are composed. This is only an unconscious feehng after 
natural methods of solving the most complex of problems, 
for it is exactly the means to which every organic thing 
has been subjected from the beginning. 

Conception of unit-characters. — The student of evolution 
now conceives animals and plants to be composed of what 
he terms ''unit-characters," analogous, roughly, to the 
atoms of the chemist. These are the smallest heritable 
units that a plant or animal may possess. Any distinct 
entity that can be traced from one generation to another, 
such as the presence or absence of pubescence on the leaves 
or stems, the height of the plant, whether dwarf or tall, 
the color of the flower or fruits, and very many others are 
now known as unit-characters. The more any group of 
plants is studied, the more definite and distinct these 
unit-characters become. The time may come when the 
gardener, from long experience, shall become acquainted 



10 Plant-Breeding 

with these quahties, so that he may synthetically put 
many units together by crossing and produce new varieties 
almost at will. 

Differences between plants and animals with regard to 
general association of "parts and their methods of reproduction. 
— Unit-characters are nature's blocks, which she uses to 
build up plants and animals into various shapes for dif- 
ferent purposes. These combinations of units when 
added together in proper extent and proportion consti- 
tute the plant and animal as we know it, the ultimate 
living and working organism, with power of growth and 
reproduction. 

In looking for the ultimate working unit, individuality or 
personality in nature, we must make a broad distinction 
between the animal and the plant. Every higher animal 
is itself a working unit ; it is one. It has a more or less 
definite span of life, and every part and organ contributes 
a certain indispensable part to the life and personality 
of the organism. No part is capable of propagating itself 
independently of the sex-organs of the animal, nor is it 
capable of developing sex-organs of its own. If any part 
is removed, the animal is maimed and perhaps it dies. 
The plant, on the contrary, has no definite or distinct 
autonomy. Most plants live an indefinite existence, 
dependent very closely upon the immediate conditions in 
which they grow. Every part or branch of the plant lives 
largely for itself, it is capable of propagating and multi- 
plying itself when removed from the parent or the colony 
of branches of which it is a member, and it develops sex- 
organs and other individual features of its own. If any 
branch is removed, the tree or plant does not necessarily 



The Fact and Philosophy of Variation 11 

suffer; in fact, the remaining branches usually profit 
by the removal, a fact which shows that there is a competi- 
tion, or struggle for existence, between the different 
branches or elernents of the plant. The whole theory and 
practice of pruning rests upon the fact of the individual 
unlikenesses of the branches ; and the unlikenesses are of 
the same kind and often of the same degree as those that 
exist between different plants grown from seeds. 

Bud-variation and hud-varieties. — The branches of a 
Crawford peach tree, for example, differ amongst them- 
selves in size, shape, vigor, productiveness, and season 
of maturity, much the same as any two or more separate 
Crawford trees, or any number of trees of other varieties, 
differ the one from the others. If any one of these 
branches or buds is removed and is grown into an inde- 
pendent tree, a person could not tell — if he were ignorant 
of its history — whether this tree were derived from a 
branch or a seed. This proves that there is no essential 
unlikeness between branches and independent plants, ex- 
cept the mere accident that one grows upon another branch 
or plant whilst the other grows in the ground. " But the 
branch may be severed and grown in the ground, and the 
seedling may be pulled up and grafted on the tree, and no 
one can distinguish the different origins of the two. And 
then, as a matter of fact, a very large proportion of our culti- 
vated plants are not distinct plants at all, in the sense of 
being different creations from seeds, but are simply the 
result of the division of branches of one original plant or 
branch. All the fruit trees of any one variety are obtained 
from the dividing up and multiplication of the branches of 
the first or original tree. 



12 Plant-Breeding 

The reader is curious to know how this original tree came 
to be, and this we may find out before we are done ; but 
for the present, let it be said that it is equally possible for 
it to have come from a seed, or to have sprung from a 
branch which some person had noticed to be very dif- 
ferent from the associated branches in the tree-top. In 
other words, the ultimate unit or individual of variation 
is the bud and the bit of wood or tissue to which it is 
attached ; for every bud, like every seed, produces an 
offspring that can be distinguished from every other 
offspring whatsoever. 



CHAPTER II 
THE CAUSES OF INDIVIDUAL DIFFERENCES 

We have now gone back to the starting-point, to that 
unit with which nature begins to make her initial differ- 
ences or individuahties ; that is, to the point where varia- 
tions arise. This point is the bud and the seed, — one 
sexless, or the offspring of one parent ; the other sexual, 
or the offspring of two parents. Now, inasmuch as the 
horticultural variety is only a well-marked variation which 
the gardener has chanced to notice and to propagate, it 
follows that the only logical method of determining how 
garden varieties originate is to discover the means by 
which plants in general vary or differ one from another. 

There is probably no one fact of organic nature concern- 
ing the origin of which modern philosophers are so much 
divided as the causes or reasons for the beginnings of 
variations or differences. It seems to be an inscrutable 
problem, and it would be useless, therefore, for us to 
attempt to discover these ultimate forces in the present 
book. Still, we must give them sufficient thought to 
enable us to satisfy our minds as to how far these variations 
may be produced by man ; and, in doing this, we must 
discover at least the underlying philosophy of plant 
variation. It is the nature of organisms to be unlike 
their parents and their birthmates. Why? 

13 



14 Plant-Breeding 

Fortuitous variation. — It will probably never be pos- 
sible to refer every variation to a distinct cause, for it is 
probable that some of them have no antecedent. If we 
conceive of the forms of life as having been created with 
characters exactly uniform from generation to generation, 
then we should be led to look for a distinct occasion or 
cause for every departure from the type ; but we know, as 
has already been pointed out, that heredity by its very 
nature is not so exact as to carry over every attribute, and 
no other, of the parent to the offspring. Plasticity is a 
part of the essential constitution of all organic beings. 
There is perhaps no inherent tendency in organisms 
towards any ultimate or predetermined completion of 
forms, as the older naturalists supposed, but simply a 
laxity or indefiniteness of constitution which is expressed in 
numberless minor differences in individuals. 

That is, some variation may be simply fortuitous, an 
inevitable result of the inherent plasticity of organisms, 
and it may have no immediate inciting cause. 

Action of natural selection on variation. — If we were to 
assume that every minor difference is the result of some 
immediate cause, then we should expect every individual 
plant or animal to fill some niche, to satisfy some need, to 
produce the definite effect for which the cause stands. 
But it is apparent to one who contemplates the operations 
of nature that very many — certainly more than half — of 
the organisms which are born are not useful to the per- 
petuity of the species and very soon perish. From these 
fortuitous variations nature selects, to be sure, many 
individuals to be the parents of other generations because 
they chance to be fitted to live, but this does not affect 



The Causes of Individual Differences 15 

the methods or reasons of their origin. It is possible that, 
whilst many of these mere individual differences have no 
direct and immediate cause, they may still be the result of 
a devious line of antecedent causes long since so much 
diffused and modified that they will remain forever un- 
recognizable ; but even so, the fact still remains that 
these present differences or variations may be purposeless, 
and it is quite as well to say that the}^ exist because it is a 
part of the organic constitution of living things that un- 
like produces unlike. 

Sex as a factor in the variation of plants. — All plants 
have the faculty, either potential or expressed, of propagat- 
ing themselves by means of buds, or asexual parts. This is 
obviously the cheapest and most direct possible method 
of propagation for many-membered plants, since it re- 
quires no special reproductive organization and energy, 
and, as only one parent is concerned in it, there is none of 
the risk of failure that obtains in any mode of propaga- 
tion in which two parents must find each other and form 
a union. There must be some reason, therefore, for the 
existence of such a costly mechanism as sex aside from 
its use as a mere means of propagation. 

It may be said that sex exists because it is a means of 
more rapid multiplication than bud-propagation, but such 
is not necessarily the fact. Many plants produce buds as 
freely as they produce seeds ; and then, if mere multipli- 
cation were the only destiny of the plant, bud-production 
would no doubt have greatly increased to have met the 
demand for new generations. The chief reason for 
the existence of sex in the vegetable world seems to be the 
need for a constant rejuvenation and modification of the 



16 Plant-Breeding 

offspring by uniting the features of two individuals into 
one. There thus arises from every sexual union a number 
of new or different forms from which nature may select 
the best, — that is, those best fitted to live in the condi- 
tions in which they chance to be placed. But whilst 
sex is undoubtedly one of the most potent sources of pres- 
ent unlikenesses, it is not necessarily an original cause of 
individual differences, since the two parties to any sexual con- 
tract must be unlike before they can produce unlike. When 
once the initial unlikenesses were established, every new 
sexual union must produce new combinations, so that 
now, when every new form, from whatever source it 
appears, comes into existence, there are other intimately 
related forms with which it may cross. This state of 
things has existed to a greater or less degree from the 
moment sex first appeared, so that the organic world is 
now endlessly varied as the result of a most complex 
ancestry. 

Physical environment and variation. — Every phase and 
condition of physical circumstances, which are not ab- 
solutely prohibitive of plant life, have plants which thrive in 
them. Every soil and climate, every degree of humidity, 
hills, swamps, and ponds, — every place is filled with 
plants. Even the trunks and branches of trees support 
other plants, as epiphytes and parasites. That is, plants 
have adapted themselves to every physical environment ; 
or, to turn the proposition around, every physical en- 
vironment produces adaptive changes in plants. There 
are those, like Weismann and his adherents, who contend, 
from purely speculative reasons, that these changes do 
not become hereditary or permanent until they have in- 



The Causes of Individual Differences 17 

fluenced a certain physiological substance which is assumed 
to reside in the reproductive regions of the organisms, 
and that all those changes which have not yet reached 
this germ-plasm are, therefore, lost, or die with the or- 
ganisms. 

Do external influences produce permanent effects in 
plants f — It is not necessary to discuss here the intri- 
cate arguments in the time-honored controversy of the 
permanent inheritance of external modifications. Such 
violent modifications as traumatic injury do not affect its 
germ cells and are not inherited. But it is the common 
experience of gardeners that the modifications of the envi- 
ronment of plants, such as changing food supply or changing 
seed from one environment to another, produce changes 
which eventually become hereditary. Whether these 
changes of environment act directly upon the germ-plasm 
to produce the change or whether they stimulate a ger- 
minal change which was otherwise latent, is a question 
which long and patient experimentation must decide. 
Certain it is, that plants have gone through a profound 
modification and it is easy to believe that environment has 
played no little part in these changes. 

Weismann teaches that ''acquired characters," or those 
variations which first appear in the life-time of the indi- 
vidual because of the influences of environment, are lost, 
because they have not yet affected the reproductive sub- 
starices ; but if these characters are induced by the effect 
of impinging environment during two or more generations, 
they may come to be so persistent that the plant cannot 
throw them off, and they become, thereby, a part of the 
hereditary and non-negotiable property of the species. 



18 Plant-Breeding 

Now, it is apparent that in one or another of the genera- 
tions which are thus acted upon by the environment, there 
must be a beginning towards the fixing or hereditable 
permanency of the new forms, and we might as well 
assume that this beginning takes place in the first genera- 
tion as in the last, since there can be no proof that it does 
not take place in either one. The tendency towards 
fixity, if it exists at all, imdoubtedly originates at the very 
time that the variation itself originates, and it is only 
sophistry to assume that the form appears at one time 
and the tendency towards permanency at another time. 
Since plants fit themselves into their circumstances by 
means of adaptive variations, we must conclude that all 
adaptive variations have the power of persisting, upon 
occasion. 

All these remarks, whilst somewhat abstruse, have a 
most important bearing on the philosophy of the origin 
of garden varieties, because they show, first that changes 
in the conditions in which plants grow introduce modifi- 
cations in the plants themselves, and second, that wher- 
ever any modification occurs it is probable that it may 
be fixed and perpetuated. 

Natal and post-natal variations. — It is necessary at this 
point that we distinguish between natal and post-natal 
variations, — that is, between those variations which are 
born with plants, and those which appear, as a result of 
environment, after the plant has begun to grow. It is 
commonly assumed that the form and general characters 
of the plant are already determined in the seed, but a 
moment's reflection will show that this is far from the 
truth. One may sow a hundred selected peas, for example, 



The Causes of Individual Differences 19 

all of which may be ahke in every discernible character. 
If these are planted in a space of a foot apart, it will be 
found, after two or three weeks, that some individuals 
are outstripping the others, although all of them came up 
equally well and were at first practically indistinguishable. 
This means that, because of a little advantage in food or 
moisture, or other circumstances, some plants have ob- 
tained the mastery and are crowding out the less fortunate 
ones. The theory and practice of agriculture rests on 
the fact that plants can be modified greatly by the condi- 
tions in which they grow, after they have become thor- 
oughly established in the soil. Plants may start equal, 
but differ widely at the harvest ; and this difference may 
be controlled to a nicety by the cultivator. Every farmer 
is confident, also, that the best results for the succeeding 
year are to be got only when he selects seeds from the best 
that he has been able to produce this year. So, given 
uniformity or equality at the start, the operator molds 
the individual plants largely at his will. 

Conception of biotypes. — Most varieties are not as 
uniform as would at first appear. A careful study of 
plants, when growing, indicates that they are not only 
modified in different degrees by environment but the plants 
themselves are not the same. They have different po- 
tentialities to begin with. Environment causes direct 
modifications to appear ; it also allows expression in differ- 
^ ent degrees of the inherent variability present. Most 
varieties of plants are polytypic, being composed of many 
distinct types, or '' biotypes" as they have been called by 
Johannsen. All this is a matter of the commonest ob- 
servation with the gardener, who is so accustomed to 



20 Plant-Breeding 

seeing great differences arise in batches of plants, all of 
which start apparently equal and with an equal chance, 
that he never thinks to comment upon the occurrence. 

Having noticed that physical environments may modify 
plants, we are now ready to consider just what changes 
in these circumstances of plant life are most fruitful in 
the production of new forms. 

Variation in food supply. — The greater part of the 
changes in the physical conditions of life hinge upon the 
relative supply of food. Climbing plants assume their 
form because, by virtue of the divergence of character, 
they are enabled to fit themselves into places that other 
plants cannot occupy. They rear their foliage into the 
air, where food and sunlight are unappropriated. The 
lower branches of tree-tops die, and the others thereby 
appropriate the more food and grow the faster. The 
entire practice of agriculture is built upon the augmenta- 
tion of the food supply. For this purpose, we set the 
plants in isolated positions, we till the ground, keep down 
other plants or weeds, add plant-food to the soil, and prune 
the tree and thin the fruit. 

Thomas Andrew Knight, the chief of horticultural 
philosophers, appears to have been the first clearly to 
enunciate the law that excess of food supply is the most 
prolific cause of the variations of plants. Darwin sub- 
scribes to it without reserve: "Of all the causes which 
induce variability, excess of food, whether or not changed 
in nature, is probably the most powerful." Alexander 
Braun, an earlier philosophical writer on natural history, 
said that "it appears rather, on the whole, as if the unusual 
conditions favorable to a luxuriant state of development, 



The Causes of Individual Differences 21 

afforded by cultivation, awakened in the plant the inward 
impulse to the display of all those variations possible 
within the more or less narrowly circumscribed limits of 
the species." It is generally agreed by those who have 
given the matter much thought, that an excess of food 
above the amount normally or habitually received is one 
of the very chief, if not the most dominant, causes of in- 
dividual differences in plants. Certainly every farmer 
or gardener knows that the richer the soil in available 
plant-food, the stronger and the more abnormal and 
unusual his product will be. 

If, then, excess of food supply is a strong factor in the 
modification of plants, and the one fundamental aim of 
agriculture is to supply food in excess of natural conditions, 
it must naturally follow that cultivated plants should be, 
of all others, the most variable. This is notably true. 
Now, the first variation that usually comes of this liberal 
food supply is increase in mere bulk. Probably every 
plant which has ever been cultivated has increased its 
stature or the size of some or all of its parts. Moreover, 
this is generally the direct object of cultivation, — to 
secure larger herbage, fruits, seeds, or flowers. Inci- 
dentally, we find here an indubitable proof of the truth 
of the hypothesis of evolution, for if it were impossible for 
plants to vary or to assume new characters, there would be 
no cultivation and no agriculture ; for there would be 
little object in cultivating a product if it grew equally well 
in the wild. 

This variation into mere bigness is more important than 
it may seem at first. All thoughtful horticulturists agree 
in thinking that the first thing to be done in ameliorating 



22 Plant-Breeding 

any plant is to ''break the type," that is, to cause it to vary. 
The particular direction of variation is not so important, 
at first ; for all experience has shown that if once the 
seedlings of a plant begin to depart from the parental 
type, other and various modifications will soon follow. If 
a plant is once strongly modified in size, variations in 
shape, color, flavor, or other attributes are forthcoming. 
This apparent accumulation of variation seems at first to 
be incapable of scientific explanation, but the reasons for 
it are not difficult to understand when once they are 
presented. 

We now ask ourselves why these many variations appear 
when once the type begins to modify itself. Consider 
the fact that the world is now full of plants. In untamed 
nature, but one more plant can grow unless another plant 
dies. All plants, therefore, are held down to narrow limits 
of numbers, and since there are so few individuals, — in 
comparison with the seeds and buds which each plant 
produces for the chance of multiplying itself, ■ — there 
must be, also, few kinds and degrees of individual dif- 
ferences. The farther and more freely a plant distributes 
itself, the greater must be the differences between various 
individuals, because they must adapt themselves to a 
wider range of conditions. All plants are held in equilib- 
rium, so to speak ; but the plant organism is plastic by 
nature and quickly responds to every touch of environ- 
ment ; so, as soon as the pressure is removed in any direc- 
tion, the plant at once springs into the breach. Recall 
the monotonous vegetation of the deep forest, where the 
battle of centuries has subdued all but the strongest. 
Clear away the forest, and then observe the fierce scramble 



The Causes of Individual Differences 23 

for place and life amongst a multitude of forms which 
spring in for an opportunity to better their conditions. 
In a few years more, the tender low herbs have gone. 
The briers and underbrush have usurped the land. As 
time goes on, one species after another perishes, and when 
the place is again reforested, two or three species hold un- 
disputed sway over the land. The poplars that followed 
the pines have long since perished and pines again dominate 
the forest. Or, if the area were turned to pasture a few 
years after the woods were removed, the herbs and bushes 
die with the browsing, and in time the June-grass covers 
the whole landscape with the mantle of conquest. So 
plants may be said to be always ready to fill new places 
in the polity of nature by adapting themselves to the new 
circumstances as they grow into them. The appearance 
of any one marked variation, therefore, is indication that 
the plant may have found a new condition, that pressure is 
somewhat lifted, and that the whole plastic organization 
may soon respond to the new environment. It is ap- 
parent, then, how the simplest and rudest cultivation has 
been able, through the centuries, so profoundly to modify 
our domestic plants that we are often unable to recognize 
the forms from which they have sprung. 

Food supply of different branches. — We must not forget 
to notice, at this point, that the food supply differs amongst 
the various branches of the same plant. Some branches, 
by reason of position with reference to the main trunk or 
with reference to air and sunlight, or, because of a better 
start in the beginning as a result of some incidental 
advantage, gain the mastery over others and crowd 
them out. We have already seen that no two branches 



24 Plant-Breeding 

on a plant are alike ; and we are now able to understand 
that sports or bud-varieties are no more inexplicable 
than seed-varieties. 

What cultivation is. — Cultivation is really but an ex- 
tension or intensification of nature's methods of dealing 
with the plant world. The ultimate result of both nature 
and man is to supply more food. The variations which 
arise from the effects of mere cultivation, therefore, are in 
kind very like those which nature produces, the chief 
differences being that of degree. The accustomed opera- 
tions of the farmer, therefore, have been powerful agents 
in the evolution of vegetable forms. The ways in which 
cultivation affords a more liberal food supply are as 
follows : — 

1. By isolating the individual plant. The husbandman 
sets each plant by itself, and then protects it by destroying 
the weeds or plants which endeavor to crowd it out. 
There is a partial exception to this in the ''sowed crops," 
like the grains, and it is noticeable that variation in these 
plants is usually less marked than in the ''hoed crops." 

2. By giving the plant the advantage of position, 
whereby it is allowed the most congenial exposure to sun 
and contour of land. 

3. By increasing the fertility of the land, either by tillage 
or the direct apphcation of plant-food, or both. Rich 
and moist soils tend to "break" the type, — or to cause 
initial variations, — to produce verdant colors and loss 
of saccharine and pungent qualities, to induce redundant 
growth, and to delay maturity and thereby to render 
plants tender to cold winter climates. 

4. By thinning the tops of plants and the fruits, whereby 



The Causes of Individual Differences 25 

the remaining parts receive an amount of food in excess 
of the habitual allowance. 

5. By divergence of character in associated plants. 
It is well known that a field planted so thickly to corn 
that it cannot grow more with profit, may still grow 
pumpkins between. The pumpkins and the corn are so 
unlike in form that they complement each other, the one 
filling the place which the other is not fitted to occupy. 
We have already seen that a copse ever so full of bushes 
may still grow vines. A meadow full of timothy may still 
grow clover in the bottom, and land covered with apple 
trees still grows weeds beneath. " The more di versed the 
descendants from one species become in structure, con- 
stitution, and habits," writes Darwin, ''by so much will 
they be better enabled to seize on many and widely diver- 
sified places in the polity of nature, and so be enabled to 
increase in numbers." 

Variation in climate. — The fact that any distinct 
climatic region usually has plants that are very closely 
related to those of other climatic regions in the same 
zone, points strongly to the probable profound modifica- 
tion of plants by climate. And, furthermore, we should 
expect that if the food environment modifies plants, the 
climatic environment must have the same power. More- 
over, there is abundant historical and experimental proof 
that climate is capable of greatly modifying the vegetable 
kingdom. There are those who contradict any great effect 
of climate in the variation of plants, and acclimatization 
has been even stoutly denied. These persons make the 
mistake of asking that a visible modification take place 
at once upon the transfer of a plant from one climate to 



26 Plant-Breeding 

another, and they also err in supposing that a plant can 
adapt itself to a cold climate only by developing a capa- 
bility to w-ithstand more cold. Indian corn is sometimes 
cited as proof that plants do not become acclimatized, 
for it is as tender to frost now as ever, for ajl that we know. 
Yet this very plant affords a most unequivocal example of 
complete acclimatization, because it has shortened its 
period of gro^i:h fully one-half whereby it escapes the 
cold of the Xorth. 

The influence on plants of a change of climate, or, 
what may amount to the same thing, the result of a trans- 
fer of plants to new climates, is so complex and so general 
that no discussion of the subject can be made at this 
time. It will answer present purposes briefl}- to designate 
the ways in which climate modifies plants: — - 

1. Climate generally modifies the stature of plants. 
They become dwarfer in high latitudes and altitudes. 

2. It modifies form. Plants tend to be broader-headed, 
and also more prostrate, in high latitudes and altitudes. 

3. Proportionate leafiness generally increases, at the 
same time. 

4. There is also often a gain in comparative fruitful- 
ness following transfer towards the poles. 

5. The colors of leaves, flowers, fruits, and seeds are 
greatly influenced by climate, there being a general 
tendency, in plants of temperate regions, to augmentation 
in intensity of colors as they are carried towards the poles. 

6. There is modification in the flavor and essential 
ingredients of various parts, following a change of climate. 

7. There is a variation in variability itself. The more 
difficult the climate in which a plant finds itself, the more 



The Causes of Individual Differences 27 

it tends to vary to meet the uncongenial en\4ronnients. 
In the high Xorth, man}' plants are so variable that the 
marks used to identify the species in other latitudes are 
often lost. 

8. There may be a profound variation or modification 
in constitution and habit by which plants become ac- 
climatized, or enabled to endure a climate at first injurious 
to them. This may occur by a variation in the constitu- 
tion of the descendants, which enables them directlj' to 
endure more untoward conditions. It generally comes 
about, however, through a change in habit, by which 
plants, when transferred towards the poles, shorten their 
season of groTsi;h or even become annuals. Plants become 
more sensitive to spring temperatures in cold climates, 
so that the}' start relativeh' much earher in the season — 
that is, at a lower sum-temperature — than in warm 
climates. Any one who has passed the springtime in both 
the Xorth and South must have noticed how much more 
suddenly the vegetation comes forward in the Xorth ; 
and it is surprising how the spring-sown crops accelerate 
their gro'^'th in the Xorth over those in the South. 

Mans control over clifnate as a means of making plants 
to vary. — The characters that result from a change of 
climatic en\aronment are peculiarh' within the control 
of the agriculturist, for a leading factor in his business 
is the transfer of plants far and wide over the earth. So 
it has come that the staple varieties of the important 
grains and fruits are unlike in Europe and America and 
in all great geographical areas, although all the various 
forms may have sprung from one ancestor within historic 
times. A new countrv is stocked with varieties from 



28 Plant-Breeding 

the mother country ; but in the course of a few genera- 
tions it is found that the varieties in cultivation are unUke 
the ones originally introduced, and from which they came. 
As wild plants have become separated from each other as 
species in the different geographical regions, so the cul- 
tivated plants soon begin to follow similar lines of diver- 
gence. In the beginning of the colonization of this 
country, for example, all the varieties of apples were of 
European origin. But in 1817, over sixty per cent of the 
apples recommended for cultivation here were of American 
origin, that is American-grown seedlings from the original 
stock. At present, probably fully ninety per cent of the 
popular apples of the Atlantic States are American pro- 
ductions. The northern states of the Mississippi Valley 
to which most of our eastern apples are not adapted, are 
now witnessing a similar transformation in the adaptation 
and modification of the varieties introduced from the East 
and from Russia. The recently introduced Japanese 
plums are conceded to be great acquisitions to our fruit- 
growing, but no doubt the best results are yet to come 
with the origination of domestic varieties of them. So 
there is an irresistible tendency towards a divergence of 
forms in different continental or geographical regions, 
and much of the inevitable result is no doubt chargeable 
to climatic environment. 

Change of seed. — We may now pause for a moment to 
consider two agencies or phenomena often associated with 
the genesis of varieties. One of these is the fact that 
the simple change of seed from one locality to another 
usually gives a larger or better product or even more 
marked variation. Mere transfer of seed is not of itself, 



The Causes of Individual Differences 29 

however, a cause of variation. The change is beneficial 
because it fits together characters and environments that 
are not in equilibrium with each other. A plant grown 
for several years in one set of conditions becomes fitted 
to them, so to speak, and it is in a state of comparative 
rest. When the plant or its progeny is taken to other 
conditions, all the adjustments are broken up, and in 
the refitting to the new circumstances new or strange 
characters are likely to appear. We shall leave this sub- 
ject for the present, expecting to give it a fuller treatment 
in a later chapter. 

Bud-variation. — Bud-variation, or sport, is a name 
given to those branches which are so much unlike the 
normal plant in any particular that they attract atten- 
tion. Many garden varieties are simply multiplications 
of such abnormal branches. This bud-variation is com- 
monly held to be such an unusual and inexplicable phenom- 
enon that it is considered apart from all the general 
discussions of variation. It is not, of course, a cause of 
variability, but only an effect of some antecedent, the 
same as seed-variation is. We have already seen that all 
the different branches, or even nodes of any plant are, 
in a very important sense, distinct individuals, since 
every one develops its own organs, each is capable of 
reproducing itself independently, and each is unlike every 
other because it is acted upon differently by environment 
and food supply. It is not strange, therefore, that some 
of these individuals should now and then depart very 
widely from the ordinary type, and thereby attract the 
attention of the gardener, who would forthwith make 
cuttings or set grafts from the part. Every branch is a 



30 Plant-Breeding 

bud-variety, just as truly as every seedling is a seed- 
variety, — since no seedling is ever like its parent, — and 
there should be no greater mystery connected with the 
sports of buds than there is with the varieties from seeds, 
for the causes that produce the one may be and probably 
are equally competent to produce the other (Figs. 6, 7). 

Struggle for life a cause of variation. — We have seen 
that the world is full of plants. There is room for more 
only as the present individuals die. Yet nearly every 
species produces a great number of seeds, and makes a 
most strenuous effort to multiply its kind. Any one 
plant, if left to itself, is capable of covering the earth in 
a comparatively short time. A fierce struggle for a chance 
to live is therefore inevitable. This conflict is most 
apparent to the general observer in the springtime, when 
every ''herb yielding seed after his kind, and the tree 
yielding fruit, whose seed was in itself, after his kind," are 
sending forth a host of sturdy offspring. The very land 
seems to be pregnant with weeds and aspiring young 
growths. But by midsummer the numbers may be 
less. The weaker and less fortunate ones have perished, 
and the victors have waxed stronger thereby. The 
annual and half of the biennial species complete their 
course upon the approach of winter, and the older peren- 
nial herbs are becoming weak ; so in the succeeding 
springtime there is again a fierce combat for the vacant 
places. 

One of the results of this conflict is the adjustment of 
plants to each other. We have seen how the climbing 
plant insinuates itself amongst the shrubberies and ties 
them together in an impenetrable tangle in order that 



The Causes of Individual Differences 31 




Fig. 6. — Couch-grass or quack-grass. Showing means of sexual propa- 
gation by seed and a sexual propagation by underground rootstocks. 
(After Clark and Fletcher.) 

it, itself, may have a chance to live. So the low plants 
of the deep forest are such as have been plastic enough to 



32 



Plant- Breeding 




Fig. 7. — Orange hawkweed. This plant can withstand the struggle for 
existence. It produces immense quantities of seed and also repro- 
duces itself by underground rootstocks. (After Clark and Fletcher.) 



adapt themselves to the damp shades. Thus plants have 
developed companionships or divergences in character, 



The Causes of Individual Differences 33 

by means of which, under the stress of circumstances, 
they are able to live together. Plants have adapted 
themselves to other plants as truly as to soil or climate ; 
and if these latter environments are ever the' sources or 
causes of variation, then the first must be also. We must 
look upon the struggle for existence, therefore, as itself 
a cause of individual differences, since we know that any 
continued pressure from without awakens an adaptive 
response in the form of the vegetable organisms. 



CHAPTER III 
THE CHOICE AND FIXATION OF VARIATIONS 

We have now seen that every living object is unlike 
every other. In plants, even every branch is unlike any 
other branch. We have endeavored to discover some of 
these universal differences. We have found that they 
are intimately associated with the welfare of the type or 
species, inasmuch as they appear, for the most part, 
to be the means of fitting the plant to live in the conditions 
in which it is placed. But we have also seen that there 
are more individuals than can find a place to live. How, 
then, does nature choose the best from the poorest (or, 
rather, the fit from the unfit), and, having chosen them, 
how does she endeavor to fix them or to make them more 
or less stable ? 

''This preservation of favorable individual differences 
and variations, and the destruction of those which are 
injurious, I have called Natural Selection or the Survival 
of the Fittest." This is the philosophy which was pro- 
pounded by Darwin, and which will carry his name to the 
last generation of men. It looks simple enough. Those 
forms which are best fitted to live, do live, because they 
crowd out the others. Yet, this simple principle of 
natural selection was the first explanation of the process 
of evolution that seemed to be capable of interpreting 

34 



The Choice and Fixation of Variations 35 

the complex phenomena of the forms of organic hfe. For 
a time, this philosophy was thought to be the one funda- 
mental motive of the evolution or progression of life, but 
we are now convinced that there are other motives or forces 
at work; but it seems to be indisputable that natural 
selection is a major force underlying the evolution of 
plants, and it is the only one with which the person who 
desires to breed plants need intimately concern himself. 

We must now determine what a variety is. This is a 
vexed question, and one which seems never to be capable 
of an answer that is satisfactory to the gardener. Time 
and again, some person has introduced what he considered 
to be a distinct new variety, only to find that other horticul- 
turists dispute him and declare that it is only some old 
variety renamed. And yet the introducer knows that 
he has not renamed an old variety, but that he has propa- 
gated a form which appeared or originated on his own 
grounds. 

What is a variety ? — Now, let us see. Nature starts 
out with the individual to make a new form. Every in- 
dividual is unlike every other one. When the individual 
differences are so well marked that we can readily de- 
scribe and distinguish them, and so permanent that they 
pass down nearly intact to a few generations, we say that 
we have a variety. If the differences are still more 
marked, we say that we have a species. Where the 
variety ends and the species begins it may be utterly 
impossible to determine ; and so we mark off at a certain 
point and say, arbitrarily, that this much is variety and 
that much is species. Asa Gray once said that ''species 
are judgments." Now, if there is no hard and fast line 



36 Plant-Breeding 

between the variety and the species, so there is none 
between the individual and the variety; for a variety is 
only the family of descendants from some one individual. 
That is, the idea of variety or species rests on difference, 
but just how much difference shall constitute one grade 
or another is a matter of individual opinion. There is 
no standardized practice. So, when two gardeners cannot 
agree as to whether a given introduction is a new variety 
or not, they are having the same kind of difficulty that two 
botanists have when they cannot decide whether two plants 
are two species or one. 

It is apparent, then, that every individual plant is 
a distinct variety, only that the differences between it and 
other individuals may be so slight that they have no 
practical utility and cannot be described and recorded. 
Just as soon as an individual plant has characters so un- 
like its kin that it has some commercial value, then the 
plant will be increased by cuttings or grafts or seeds, 
the brood of offspring will be given a name, and a new 
variety is born. 

Individuals with the same general features may appear 
simultaneously in two or more places, and two or more 
men may propagate, name, and introduce them. When 
they are all brought together and compared, it will be said 
that they are all the same variety, that, according to the 
rules of nomenclature, the brood which chanced to be 
named first must ''stand" or be held to be the type of the 
variety and the other names must become synonyms. 
Yet some persons may discover minor differences in them 
and demand that the variety be kept distinct. So the 
see-saw goes on — a variety is a variety so long as it an- 



The Choice and Fixation of Variations 37 

swers some purpose in use or trade, and it is not a variety 
when it is so much like some other variety that it has no 
merit that the other does not possess. 

As soon as a plant appears with some features which 
are more desirable than anything that has preceded it, 
therefore, it may be the beginning of a new variety. Man 
chooses it, and then propagates it. This is human selec- 
tion. If nature did the same thing, it would be natural 
selection. 

It must not be understood that there are no definite 
species in nature. Some plants are so distinct, and so 
constant in their characters, as to leave no doubt. But 
wide variability is very common, and it may obscure the 
relationship. 

Adaptation in nature. — Now, how does nature preserve 
or fix this type? She does not preserve it. She simply 
chooses it as a beginning and gradually modifies it and 
shapes it into the form which she needs. She has no 
permanent forms. There is a general onward progression 
of one type either towards other types or towards ex- 
tinction. We have seen that nature is constantly choosing 
and selecting. If she selects an individual for the be- 
ginning of a race, then she selects just as keenly from every 
offspring of that individual, and so on to the end of time. 
The process never stops. So nature fixes her forms by 
keeping them moving, growing, constantly developing 
farther away from their beginnings. 

The vexed question as to whether there is an accumula- 
tive effect in variation, need not be considered here, as it 
is foreign to the particular point of view at this place. 

Artificial selection. — Now, man does the same thing. 



38 Plant-Breeding 

A plant in a cabbage row pleases him. It has a solid 
small head and stout stem. He stores it away for seed. 
Amongst the offspring, perhaps fifty per cent are as good 
as the parent. These are saved. So the process goes 
on, from season to season. In four or five generations 
of plants, he finds that ninety per cent of the seeds '^come 
true." Then he names it and introduces it. It is well 
advertised in the seed catalogues. Many persons buy the 
seeds. Some of these persons will grow their own seeds, 
and every one of them has a different ideal in mind when 
selecting the seed parents. So, in the course of a few 
years it is found that there are really several more or less 
different forms under the same name. Some persons may 
observe this difference and legitimately introduce one or 
more of the forms as distinct varieties. Some other 
person, however, who has known the history of the stock 
and who is not aware that varieties pass into other forms, 
objects to the new names and declares that the introducer 
is imposing on the public. 

This is the history of ninety out of every hundred 
varieties which are habitually propagated by seeds, like 
the kitchen-garden vegetables and the annual flowers. 
Some peculiar individual, appearing we know not why, is 
discovered, and seeds are saved and selection — perhaps 
unconscious selection — begins. After a time the variety 
is broken up into several, or else, if it varies only slightly, 
into divergent forms, the whole body or generations of 
the variety move onward, gradually departing from the 
initial type until it is no longer the same, although it 
may bear the same name. The life of seed varieties, in 
their pure and original forms, is very short. Even the 



The Choice and Fixation of Variations 39 

best of them are usually measured by a score of years or 
less. They run out or pass out by variation, into other 
forms. The Trophy tomato is not the Trophy tomato 
which was introduced over forty years ago, although it bears 
the old name and is a direct descendant of the first stock. 

Bud selection. — In plants multiplied by buds — that is, 
by budding, grafting, cuttings, tubers, and the like — 
there is less variation in the offspring than in those prop- 
agated by seeds. Yet we have seen that no two Baldwin 
apple trees — all of which are but divisions, more or less 
remote, of the same original tree — are alike, and now 
and then one branch of a fruit tree may '^ sport " or develop 
a strange bud-variety. We know, also, that the same 
variety of fruit tree takes on different characters in 
different geographical regions, so that the Greening apple 
is no longer the Greening of Rhode Island in the West 
and South. So, it is apparent that even when we divide 
a plant into many parts and distribute the members far 
and wide, and when there is no occasion for concerning 
ourselves with fixing the type, — even here there is 
variation. In some cases, particularly in those in which 
we multiply the plant by dividing abnormally developed 
parts, there is a tendency to scatter or to vary in many 
directions, and also a tendency to run out by degeneration. 
This is admirably true of the potato, varieties of which, 
in ten years or less, become so mixed in their characters, 
through rapid variation and deterioration, that we must 
return to seedling productions for a new start. 

Variation and selection not entirely within man's con- 
trol. — Man is only rarely the direct means of originating 
variations. He finds them among the normal plants of 



40 Plant-Breeding 

the fields and gardens. His skill and science are exercised 
in the selection and so-called breeding of the offspring, 
more than in the original genesis of the new form. It is 
usually only in those plants which he multiplies by simple 
division that he gains much immediate profit by crossing 
or hybridizing. It is the slow and patient care and selec- 
tion, day by day, which permanently ameliorates and 
improves the vegetable world. Nature starts the work; 
man may complete it. 

It is now generally held that species in nature some- 
times originate suddenly, by means of ''leaps." In fact, 
the de Vriesian view is that real species so originate, 
and the steps whereby a few species come into existence 
are called mutations. (See Chapter V.) However this 
may be, it is nevertheless true that these mutations are 
yet beyond the power of man directly to produce. Selec- 
tion is still a powerful agent with which to ameliorate 
domestic plants. 



CHAPTER IV 
THE MEASUREMENT OF VARIATION 

It is often desirable to describe a plant or a group of 
plants in exact mathematical terms. Most of the plant 
characters with which a breeder deals are measurable, 
and an individual plant may be described as having so 
many leaves, so many grains, and so on throughout a 
long list of measurements ; or a group of plants may be 
expressed in the form of averages ; likewise, the degree 
of resemblance or difference between plants and their 
offspring, or among plants of a certain group or ''popula- 
tion. " The degree or extent of correlation or association 
of plant characters may also be expressed mathematically. 

The science of biometry. — The expression of variation 
and heredity by means of statistical methods is known as 
the science of Biometry. This method of description is 
now being widely employed by experimental plant-breeders. 
It is another tool which the breeder uses to record his 
progress and describe his plants. The biometrician 
should be cautioned to keep his use of mathematical 
treatment subservient to the biological facts, not forgetting 
that biometry is simply a means toward an end and not 
an end in itself. It is better first of all to become ac- 
quainted with the real plants before any mathematical 
treatment of their variability is attempted. It is often 

41 








to 


•0 


•0 


o 

CVJ 
42 





The Measurement of Variation 43 

desirable, however, to treat plants in groups by means of 
statistical generalizations. 

■ Type. — In the study of any group of plants, called a 
"population," whether it be corn, wheat, the ray-florets 
of daisies, or what not, the breeder has in mind a certain 
type around which the individuals tend to center. 

The corn breeder has in mind a certain length of an ear 
of corn which is his ideal type. He chooses ears of this 
length and plants them in his plat, and at harvest time 
what does he get ? Not all ears of this length, but ears 
ranging above and below this length. The offspring will 
be distributed, in all probability, above and below this 
parental type and may possibly reach the upper and lower 
limits of the race. There will be a group near the average 
which will contain a larger number of individuals than 
any other and thus we have another conception of type. 
There is the ideal parental type which the breeder has in 
mind, and another type, probably different, shown by the 
offspring. To find the latter, the ears of corn are care- 
fully measured and their average length determined. 
This average constitutes a concrete mathematical expres- 
sion for the type of the offspring. 

BiometricaL expression of variability. — The amount and 
range of variability may also be well expressed statistically. 

As an illustration, a number of pea plants were measured 
and their height was found to range from 5 to 30J inches. 
A few were short and a few were tall, but most of the plants 
were of average height. For the sake of convenience, the 
plants having similar measurements were placed together 
in one class. When all the results had been brought 
together they appeared as in the following table : — 



44 Plant-Breeding 

_T T Number of Individ- 

Height IN Inches ^^ls in Each Class (/) 

5.1- 6.5 1 

6.6- 8 4 

8.1- 9.5 6 

9.6-11 29 

11.1-12.5 30 

12.6-14 37 

14.1-15.5 39 

15.6-17 43 

17.1-18.5 34 

18.6-20 26 

20.1-21.5 18 

21.6-23 8 

23.1-24.5 5 

24.6-26 2 

26.1-27.5 2 

27.6-29 1 

29.1-30.5 1 

286 

Here we have what is called a ''frequency distribution," 
representing the crop as it falls into the different groups. 

The curve in Fig. 8, known as the ''Quetelet curve," 
represents the results graphically. 

The frequencies, that is, the number of times each 
measurement appears (see column / in the table), are 
plotted on the axis of ordinates, line A-C, and the classes 
on the axis of abscissas, line C-B. For the purpose of 
plotting and working the data the mid-class is used, that 
is, 5.8 inches instead of 5.1-6.6 inches, and so forth. 

Mode. — We see by inspection of the foregoing data 
that there is one group of the most common height, that is, 
there are more plants having a height of 15.6 to 17 inches 
(16.3) than any other class. 

The group containing the greatest number of plants, 



The Measurement of Variation 45 

that is, of the greatest frequency, is called the mode. 
It is an excellent expression of type. When the group of 
plants or population which is being studied is measured 
and arranged with some suitable grouping, as illustrated 
here, we see what the variety tends to do on the whole. 

Modal coefficient. — It is desirable to know what per- 
centage of the individuals falls into this group of highest 
frequency, called the mode. This can be readily found by 
dividing the number of individuals in this class (43) by 
the total number (286) and multiplying by 100. This is 
called the modal coefficient, and denotes the percentage of 
individuals conforming to type. This modal coefficient is 
.15 or 15%; that is, fifteen per cent of all of the plants 
in this variety are found in one class. 

However, as this is dependent on the system of measure- 
ment, one modal coefficient is not directly comparable 
with another unless the same practice of measurement has 
been used. Moreover, one could not compare the modal 
coefficient of height directly with that of weight or any 
other character of a different nature. 

It may readily be seen that a knowledge of the distribu- 
tion of plants as represented by the mode or modal coeffi- 
cient is of scientific and practical importance. It enables 
the breeder at any time to spread out before himself a 
fair representation of his variety. He can see at a glance 
what is the prevaifing type and in what direction and to 
what degree his breeding is extending. 

Mean. — There is another conception of type known 
as the mean or average. One can understand that the 
average height will differ in most cases from the 
commonest height. The mean is most easily obtained by 



46 



Plant-Breeding 



multiplying the mid-value of each class, say 5.8, by the 
number in that class, adding their products, and dividing 
by the total number of individuals. This is expressed 



by the formula M (mean) 



_S/F 



n 



where V represents the 



variables, / the frequency of each variable, n the total 
number of individuals, and 2 the summation of fV. 



Mean. — 


V 


/ 


fV 




5.8 


1 


5.8 




7.3 


4 


29.2 




8.8 


6 


52.8 




10.3 


29 


298.7 




11.8 


30 


354.0 




13.3 


37 


492.1 




14.8 


39 


577.2 




16.3 


43 


700.9 




17.8 


■ 34 


605.2 




19.3 


26 


501.8 




20.8 


18 


374.4 




22.3 


8 


178.4 




23.8 


5 


119.0 




25.3 


2 


50.6 




26.8 


2 


53.6 




28.3 


1 


28.3 




29.8 


1 


29.8 




n = 286 


2 = 4451.8 


Mnnn.(S/F) 


4451.8 . 


.^ .^ inohps. 





n 



286 



Use of mean. — The mean gives a good average value 
of the character and is often more useful than the mode 
in expressing type. The breeder must use his judgment 



The Measurement of Variation 47 

as to which should be used in each case, the mean or the 
mode. 

Mathematical expression of variability. — After the 
average or mean of any group of plants has been deter- 
mined, it is desirable to know the amount of deviation of 
the different individuals from the mean. This determina- 
tion gives a concrete expression which is an index of the 
amount of variabiHty exhibited. This variabiUty is ex- 
pressed as the average deviation or the standard deviation. 
The latter is ordinarily employed by mathematicians. 

Average deviation. — The average deviation is deter- 
mined by obtaining, first of all, the amount which each 
class varies from the mean and multiplying each deviation 
by the number of individuals concerned. For example, 
the column D is obtained by finding the difference between 
the mean, 15.5, and the variations in column T^ : thus 
in the first case the difference between 5.8 and 15.5 is - 9.7 
while farther down column V we find 16.3, which is greater 
than the mean, giving us a value of 0.8 in column D. 

Now, if there were the same number of individuals in 
each class, the average deviation could be found by adding 
up the deviations in column D, and dividing by the total 
number of individuals in column /, but there is one indi- 
vidual deviating - 9.7 while there are 43 deviating 0.8 
and 18 deviating 5.3, and so forth. In order to overcome 
this the deviations are multiplied by the number of in- 
dividuals giving the column fD. The sum of this column 
divided by the total number of individuals gives the 
average deviation. This is an index of variabiHty. 
The average deviation is expressed by the following 
formula : — 



48 



Plant-Breeding 



Average deviation = 



2D/ 



n 



Standard deviation. — The operations for finding the 
standard deviation are the same as for the average devia- 
tion except that the deviations in column D are squared 
before multipl3dng by the frequency numbers (/), thus 
giving the columns D^ and D^f respectively. The sum 
of the latter divided by the total number of individuals 
and the square root of the result extracted gives the 
standard deviation. This can be expressed by the follow- 
ing formula : — ^ T^2f 

ar= =^* 

n 

The details of determining the average and standard 
deviation are as follows : — 



V 


/ 


D 


fD 


Z)2 


D^f 


5.8 


1 


- 9.7 


9.70 


94.09 


94.09 


7.3 


4 


- 8.2 


32.80 


67.24 


268.96 


8.8 


6 


- 6.7 


40.20 


44.89 


269.34 


10.3 


29 


- 5.2 


150.80 


27.04 


784.16 


11.8 


30 


- 3.7 


111.00 


13.69 


410.70 


13.3 


37 


- 2.2 


81.40 


4.84 


179.08 


14.8 


39 


- 0.7 


27.30 


0.49 


19.11 


16.3 


43 


0.8 


34.40 


0.64 


28.12 


17.8 


34 


2.3 


78.20 


5.29 


179.86 


19.3 


26 


3.8 


98.80 


14.44 


375.44 


20.8 


18 


5.3 


95.40 


28.09 


505.62 


22.3 


8 


6.8 


54.40 


46.24 


369.92 


23.8 


5 


8.3 


41.50 


68.89 


551.12 


25.3 


2 


9.8 


19.60 


96.04 


192.08 


26.8 


2 


11.3 


22.60 


127.69 


255.38 


28.3 


1 


12.8 


12.80 


163.84 


163.84 


29.8 


1 


14.3 


14.30 
925.20 


204.49 


204.49 




n=286 


2 = 4851.31 



The Measurement of Variation 49 



925 20 
Average deviation = ^ = 3.24 inches. 



Standard deviation, (o-) = -y/ — !^ = 4.1+ in. 

Coefficient of variability. — The average deviation or 
standard deviation as outlined above is always determined 
in the denomination of the unit in which the plant is 
measured ; if it is height of plant in inches, the deviation 
will be in inches and so forth. This prohibits the careful 
comparison of the deviations of different plants or parts 
of a plant because some deviations may be in pounds 
or others in inches, and hence they will not be directly 
comparable. 

It is desirable, therefore, to have an abstract expression 
so that the relative amount of variabiUty of one class of 
organs may be directly compared with the variabihty of 
another. This is called the coefficient of variability. It is 
found by dividing the standard deviation by the mean. 
Thus an abstract number is found which expresses the 
variability. In our case the standard deviation = 4.1 
inches and the mean = 15.5 inches, so that 

^^ = .264 = 26.4 % = the coefficient of variabihty. 
15.5 

If the coefficient of variabihty of the weight of the plants 
had to be determined and was found to be, say, .384, it 
would follow at once that the height of the plant was 
considerably more variable than the weight. 

The coefficient of variabihty may be expressed as 
follows : — 



50 Plant-Breeding 

C = -^x 100. 
M 

Probable error. ^ — It is obvious that these mathematical 
expressions of type and variability will be modified some- 
what by the number of individuals measured. The 
greater the number of individuals employed, the less the 
error. These differences which arise from the fewness 
of individuals employed is known as the probable error. 
It is expressed by a pair of divergences {=^ E), the one 
above and the other below the actual value found, and 
indicates that the chances are even that the true value 
lies somewhere between the value found plus the error 
and the value minus the error. For example, the probable 
error of the mean in the problem here cited is =•= .016 and 
is found by the formula given below. This means that 

1 Formulae for probable errors : — 

ET _i_ ^T^c standard deviation . ^^^-f 

E mean = =•= .6745^ ^ — 7-^ -, or ± .674o- 

number of individuals n 

E standard deviation = ± .6745 standard de _viation ^ ^^ 



.6745 



V 2 X number of individuals 



E coefficient of variability = =fc .6745 



V2n 

coefficient of variabilitv 



= ± .6745 

V2n 



V 2 X number of individuals 
C 



But when C is greater than 10% use the formula 

EC = ^ .6745— ^ri+2f— VT 



The Measurement of Variation 51 

the true mean is probably somewhere between 15.5 + .016 
and 15.5 — .016 or between 15.516 and 15.484. The size 
of the error is generally indicative of thje number of the 
individuals employed and the general dependability of the 
work. 

Use of statistical methods. — The use of statistical 
methods enables the breeder to express quite accurately 
the amount of variability which would otherwise be 
expressed with considerable difficulty. It enables him 
also to keep an accurate record of his work from year to 
year and affords him a convenient method of comparing 
one year's crop with another. 

It will be seen later that statistical methods may also be 
employed to express correlation and extent of inherit- 
ance. 



CHAPTER V 
MUTATIONS 

There is endless dissimilarity in nature. No two 
plants and no two animals are exactly alike. There are 
more plants and animals than can find a place in which 
to live and thrive. There results a struggle for existence. 
Those animals or plants which, by virtue of the individual 
differences or pecuUarities, are best fitted to the condi- 
tions in which they are placed, survive in this struggle 
for existence. They are " selected to live." Those that 
survive, propagate their pecuharities. By virtue of 
continued variation, and of continued selection along a 
certain line, the peculiarities may become augmented; 
finally the gulf of separation from the parental stem 
becomes great, and what we call a new species has origi- 
nated. 

Evolutionary theories of Darwin and de Vries. — This, 
in epitome, is the philosophy of Darwin in respect to evolu- 
tion of organic forms. It contains the well-known postu- 
late of natural selection, the principle that we know as 
Darwinism. This principle has had more adherents 
than any other hypothesis of the process of evolution. 
All recent hypotheses in some way relate to it. A number 
of them modify it, and some dispute it. The most pro- 
nounced counter-hypothesis is also the newest. It is that 

52 



Mutations 



53 



of Professor de Vries, botanist, of Amsterdam, Holland, 
who denies that natural selection is competent to produce 
species, or that organic ascent is the product of small 
differences gradually enlarging into great ones. According 
to de Vries' view, species-characters arise suddenly, or 
all at once, and they are ordinarily stable from the moment 
they arise. 





-i 6-10 10-16 l&-iO 20-2J 26-SO S0-3i i^-*0 4(M6 



70-7S 7i-«0 eu-bi Sj-OO 1I0-SI5 O'ylOO iOO 



Fig. 9. — Variations in statures of (Enothera nanella (left), a mutant, 
and (Enothera Lamarkiana (right), its parent. Oenothera nanella : 
Range, 7-35 cm. ; M., 22.81 ± 1.02 cm. ; <t, 7.26 ± 0.72 cm. ; C. V., 
31.84=^3.16 per cent. (Enothera Lamarkiana: Range, 77—96 cm.; 
M., 88.68 ± 0.55 cm. ; <t, 4.76 ± 0.39 cm. ; C. V. 5.37 ± 0.44 per 
cent. 



De Vries conceives that variations, or differences, are of 
two general categories : (1) Variations proper, or small, 
fluctuating, unstable differences pecuUar to the individual 
(only partially transmitted to offspring) ; and (2) muta- 
tions, or differences that are usually of marked character, 
appear suddenly and without transition to other forms 
and are at once the starting-points of new species or races. 
Variations proper may be due to the immediate environ- 



54 



Plant- Breeding 



ment in which tlie plant Uves. The mutations arise from 
causes yet unkno^vn, although these causes are considered 
to be physiological. Probably many so-called mutations 
are hybrids and hence not mutations in the strictest 
sense. 

Differences between fluctuating variations and mutations: — ■ 

1. Fluctuating variations are very common and are 
to be found in all plants and animals. Mutations occur 
intermediately and are rare. 

2. Fluctuating variations are thought not to be trans- 

mitted. ]\Iuta- 
tions are trans- 
mitted. 

3. Fluctuating 
variations pre- 
sent a series of 
differences which 
may be plotted 
on a frequency 
curve and obey 
the laws of 
chance. ]\Iuta- 
tions or saltatory 
variations do not 
obe}" the laws of 
chance, and can- 
not be plotted in 
the form of a 
frequency curve. 
4. Fluctuating variations do not lead to a new perma- 
nent mean of the race. Mutations cause a new mean to be 




lis 12 IIS IJ OLJ /fr 7W IS liJ 16 16.5 n ns IS 18J 19 

Fig. 10. — Variations in the amount of sugar 
in 4t),000 beets. 



Mutations 



55 



formed, around which is grouped a new series of fluctuating 
variations, forming a frequency curve. (See Fig. 9.) 

5. In a fluctuating variation no new unit characters are 
added. The same char- 
acters are merely found 
in greater or less quan- 
tity or number (Fig. 10) . 
Where a mutation oc- 
curs, new unit charac- 
ters are added or old 
ones lost. 

6. Fluctuating vari- 
ations represent indi- 
viduals or parts of them. 
Mutations represent 
groups of individuals. 

In fluctuating vari- 
ations, the small differ- 
ences are grouped 
around what may be 
called a '^center of fluc- 
tuation," which is the 
mean of the frequency 
curve. When a mutation is formed, a new center of 
fluctuation is established around a new mean. 

History of mutation. — The first mutation was recorded 
in 1590. In the garden of Sprenger, an apothecary of 
Heidelberg, was found a peculiar form of Chelidoniwn 
majus. The new form appeared suddenly and without 
intermediates from a lot of plants which had been culti- 
vated for many years. This mutant had ''leaves cut into 




Fig. 11. — Chelidonium majus. 



56 



Plant-Breeding 



narrow lobes with almost linear tips, and the petals were 
also cut up." The new species has been constant since 
the first, and follows Mendel's law when crossed with 

C. majus, its par- 
ent. (See Figs. 
11 and 12.) 

The word 
'' mutation" was 
first used in 1650 
by Dr. Thomas 
Browne, in his 
book ^'Pseudo- 
doxia Epidem- 
ic a .' ' Lock 
quotes from 
Book VI, Chap- 
ter X, ^'Of the 
Blackness of Ne- 
groes," as fol- 
lows : — 

''We may say 
that men become 
black in the same 
manner that 
some foxes, squir- 
rels, lions, first turned of this complexion, whereof there 
are a constant sort in diverse countries ; that crows 
became pyed, all which mutations, however, they began, 
depend upon durable foundations and such as may con- 
tinue forever." 

History of the appearance of double flowers. — Double 




Fig. 12. — Chelidonium laciniatum. A flower of 
it to the left. Below a flower of C. tnajus. 



Mutations 



57 



flowers which have persisted for a long time are thought to 
be mutations from single types. Some of the first re- 
corded appearances of double flowers were described in 

1671 by Abraham Hunting in a 
book called, ''Waare Oeffeninge 
der Planten" or "True Exercises 
with Plants." This large book 
on garden plants contained a 
long Hst of double flowers which 





Fig. 13. — Anemone coro- 
naria, single-flowered 
form. 



Fig. 14. — Anemone coronaria, semi- 
double-flowered form. 



were found growing in gardens at that time. Double 
flowers of such plants as poppies, hver-leaf (hepatica), 
wallflowers (cheiranthus) , violets, caltha, althea, colchium, 
and periwinkle {vinca), were described. 



58 



Plant-Breeding 



Other double forms have since been added. The double 
marigold {Chrysanthemum indicum) came from Japan; 
double zinnias from Mexico ; and double dahlias which 
were first produced in Belgium in 1814, are examples. 

The garden anemone {Anemone coronaria) is said to 
have been first found double in an EngUsh nursery in 
the first half of the last century. One flower with a single 

broadened stamen was 
observed by WilKam- 
son, owner of the nurs- 
ery. The seed from this 
was saved separately 
and planted the next 
year. After a few gen- 
erations of selection of 
this kind, the double 
flowers appeared as mu- 
tations and bred true to 
type (Figs. 13-15). 

The origin of the 
double petunia dates 
back to the year 1855, 
when it suddenly arose from ordinary seed in a garden 
at Lyons. Carriere reported that from this one plant 
all double races and varieties of petunias have been 
derived by natural and partly by artificial crosses, and 
he added that hkewise other species were known at that 
time to produce new double varieties rapidly. 

Geoffroy St. Hilaire, about 1825, expressed his belief 
in saltatory variations as a means of evolution. He 
thought that evolution does not take place entirely by 




Fig. 15. 



— Anemone coronaria, var. flore- 
pleno. (Full double.) 



Mutations 



59 



the slow changes advocated by Lamark. His ideas were 
theoretical, however, and at that time were not borne out 
by experimental evidence. 

Darwin recognized the appearance of sudden variations 
of a marked character, such as is seen in the origin of 
large-crested PoHsh fowls and short-legged Ancon sheep. 
He thought that these new and strange forms would be 
lost soon by intercrossing and, being rare, that they pos- 
sessed no value. He held that the slow accumulation 
of minute fluctuating variations was the important factor 
in evolution. 

De Vries' experiment with Oenotheras. — De Vries became 
convinced long ago that Darwin's theory of the origin 
of species through ac- 
cumulation of minute 
changes was not the only 
means of creating new 
types. He determined 
to produce mutations ex- 
perimentally, if possible. 
His results in the forma- 
tion of a new variety of 
the corn marigold will be 
described later. After 
making preliminary ex- 
periments with some 
hundred species, de Vries 

finally decided upon (Enothera Lajnarkiana as the most 
suitable form to use (Figs. 17 and 18). ''Only one of my 
tests met with expectations. This species proved to be 
in a state of mutation, producing new elementary forms 




Fig. 16. — Hugo de Vries. 



60 



Plant-Breeding 



continually, and it soon became the chief member of my 
experimental garden. It was one of the evening prim- 
roses/' This (E. Lamarkiana was found to produce a 
large number of mutants, both when growing wild and 
under cultivation. 

The (E. Lamarkiana plants which became the basis of 




Fig. 17. — (Enothera Lamarkiana and (Enothera nanella in bloom. 



future experiments were found growing wild in a field at 
Hilversum, near Amsterdam, Holland. Little is known 
of its history except that it is a native of America. It has 
not been found growing wild in America in recent years, 
although there seems to be evidence that it was seen and 
collected in the Southern States in the last century. The 
near relatives of (E. muricata, which were very common in 
the sandy regions of Holland, are very stable ; de Vries 



Mutations 



61 



found no appreciable change in them, although he watched 
them for more than forty years. 

Lamark's evening-primrose is grown in Europe as a cul- 
tivated plant, used principally for ornamental planting. 
It seeds abundantly and some of the plants have escaped 
cultivation. Groups of plants are found growing wild 
in many places. These wild plants remain in groups 
rather than being widely scattered, suggesting a definite 




V K n tS tl> XO Xr ZZ Z3 »r ZS 2e 27 ZS 29 JO si'jX 33 Jt.Hhu, 



Fig. 18. — (Enothera Lamarkiana. Curve exhibiting variations in the 
length of fruits of 568 plants. The dotted line is that given by 
Quetelet-Galton Law. 



origin for each group. (E. Lamarkiana is described as a 
''stately plant with a stout stem, attaining often a height 
of 1.6 meters and more. When not crowded, the main 
stem is surrounded by a large circle of smaller branches, 
growing upwards from its base so as often to form a dense 
bush. These branches in their turn have numerous 
lateral branches. Most of them are crowded with flowers 
in summer, which regularly succeed each other, leaving 
behind them long spikes of young fruits. The flowers are 



62 Plant- Breeding 

large and of a bright yellow color, attracting immediate 
attention, even at a distance. They open towards 
evening, as the name indicates, and are pollinated by 
bumble-bees and moths. On bright days their duration 
is confined to one evening, but during cloudy weather they 
may still be found open on the following morning. Con- 
trary to their congeners, they are dependent on visiting 
insects for pollination. 

''In (E. Lamarkiana no self-fertilization takes place. 
The stigmas are above the anthers in the bud, and as the 
style increases in length at the time of the opening of 
the corolla, they are elevated above the anthers and do 
not receive the pollen. Ordinarily the flowers remained 
sterile if not visited by insects or pollinated by myself, 
although rare instances of self-fertilization were seen." 

(E. Lamarkiana is a biennial, producing rosettes in 
the first year and stems in the second year. This species 
was found to be variable in all periods of its life cycle, — 
in the seedlings, the rosettes, and the stems. 

De Vries pursued three methods in obtaining his muta- 
tions : — 

1. Observations and studies of the plants while growing 
in the wild state in the fields. 

2. Some of the plants were removed from the wild state 
and placed under cultivation. Many of the plants were 
self-fertilized and their seed sown under controlled con- 
ditions. By this method several mutants were found 
which were too weak to withstand the competition of field 
conditions. 

3. Repetition of the sowing process for several genera- 
tions, leading to the production of new forms. 



Mutations 



63 



De Vries divided the new types of plants into five groups, 
classified as follows : — 

1. Retrograde varieties witli 'negative attributes, 
(E. Icevifolia, (E. brevistylis, and (E. nanella (Figs. 17 
and 19). 




Fig. 19. — (Enothera lata (left), (Enothera Lamarkiana (middle), 
CEnothera nanella (right). 

2. Progressive elementary species possessing new 
characters, and appearing as vigorous as the parent plant, 
CE. gigas and (E. ruhrijiervis. 



64 Plant-Breeding 

3. Progressive elementary species, which are weaker 
than the parent species, CE. albida and (E. ohlonga. 

4. Organically incomplete forms, (E. lata (Fig. 19). 

5. Fertile but inconstant species forms, CE. scintillans 
and (E. elliptica. 

The new species and varieties may be described as 
follows : — 

Group I, retrograde varieties, which have lost some 
of the characters possessed by the parent, (E. Lamarkiana : — 

(E. Icevifolia is easily distinguished from its parent, 
(E. Lamarkiana, by having smooth, bright leaves, without 
undulations. These leaves are narrower and more slender 
than in Lamarkiana and the flowers of the brighter yellow. 
This variety was constant from seed, showing no reversion. 
It is a strong-growing plant and perfectly fertile. 

CE. brevistylis is a short-styled form. The ovarj^ of 
this plant is abnormally situated and is not conducive to 
proper fertilization. The ovary is reached by only a few 
pollen tubes and fertilization must be incomplete. The 
few seeds that are obtained reproduce this type without 
reversion to Lamarkiana. CE. brevistylis may be dis- 
tinguished from the other forms before blossoming as 
the buds are much shorter and thicker than in the other 
species. The presence of leaves more rounded at the 
tip also distinguishes this form from others before 
flowering. 

CE. nanella is a dwarf form, attaining often only one- 
fourth the height of the other types. The flowers on this 
dwarf form are as large as upon Lamarkiana, which is a 
striking feature. The size of the leaves is proportionate 
to the height of the plant, but retain the same form as the 



Mutations 65 

parent species. The stems are unbranched and very 
brittle. (E. nanella is frequently produced as a mutation 
and is absolutely constant (Figs. 17 and 19). 

Group II, progressive elementary species, possessing new 
characters : — 

(E. gigas is a giant form which is much larger in every 
respect than its parent, except in height. The stems are 
much larger ; internodes are shorter and the leaves more 
numerous than the parent species (CE. Lamarkiana). 
The flower-buds are large and closely crowded on the 
spike, and when the flowers open, they make a beautiful 
appearance (Fig. 20) . 

(E. ruhrinervis is characterized by the red veins and red 
streaks on the fruits. This plant is as tall as (E. gigas, 
but a little more slender. A feature of this type is the 
brittleness of the leaves and stems, especially in the annual 
individuals, of which many are found. 

Many of these mutants may be recognized before the 
adult stage has been reached, for example, at about the 
age of two months. The leaves of (E. gigas are broad, of a 
deep green, the blade sharply cut off from the stalk, all 
of the rosettes becoming stout and crowded with leaves. 
In (E. ruhrinervis, on the contrary, the leaves are thin, 
of a paler green, and with a silvery white surface ; the 
blades are in the form of an ellipse, acute at the apex, 
and gradually narrowing into the petiole. 

Both of these species are quite constant and do not 
revert to (E. Lamarkiana. However, other mutants have 
sprung from these two species, especially from ruhrinervis, 
which is produced in greater numbers from Lamarkiana 
than is gigas. 




jTiG. 20. — A, spike with almost ripe fruits of (Enothera gigas, a mutant 
species ; B, the same of (Enothera Lamarkiana, its parent form. 

66 



Mutations 67 

Group III, progressive elementary species which make a 
very weak growth : — 

CE. alhida has whitish, narrow leaves, apparently in- 
capable of producing sufficient quantities of organic food, 
and hence are very weak. These plants are not suffi- 
ciently robust to withstand competition in the field and 
require transplanting into rich soil in pots in order to 
allow them to live through the first year so that they 
can produce seed the second year. When these seeds 
are planted they produce individuals true to type. 

(E. oblonga is a small plant about half the size of Lamark- 
iana and may be grown either as an annual or as a bien- 
nial. It is characterized by its narrow leaves, which are 
fleshy and of a bright green color. Another striking 
feature of this type is the presence of numerous little 
capsules covering the axis of the spike after the fading 
away of the petals. (E. oblonga is very constant if grown 
from pure seed. 

The forms already described are relatively very con- 
stant and never revert to the parent form. Contrasted 
with these constant forms, de Vries found several incon- 
stant types as follows : — • 

Group IV, organically incomplete types : — 

CE. lata is characterized by the fact that only pistillate 
flowers are formed. The anthers seem to be robust, 
but they are dry, wrinlded, and nearly devoid of contents. 
It is a low plant with very dense and luxuriant, but brittle, 
foliage. It has bright yellow flowers which open only 
partially and remain wrinkled throughout the flowering 
time. CE. lata may be recognized by its seedlings, which 
have leaves of a nearly orbicular shape and are very 



68 * Plant-Breeding 

sharply set off against the stalk. The mature plant 
has broad sinuate leaves with rounded tips, which are 
often crowded together on the summits of the stems and 
branches to form rosettes. (E. lata may be considered 
a true mutation, and when crossed with CE. Lamarkiana, 
the progeny of the second generation segregates into 
mendelian proportions, lata being recessive (Fig. 19). 
Group V, perfectly fertile but inconstant species : — 
CE. scintillans is characterized by the production of 
deep green leaves with smooth, shiny surfaces, ''glisten- 
ing in the sunshine." The plants are smaller and less 
branched than the parental type. CE. scintillans is a 
very inconstant form ; from the seeds which are produced 
in great numbers, there results not only scintillans, but 
Lamarkiana, oblonga, lata, and nanella, with a predomi- 
nance of the parental Lamarkiana. In regard to its in- 
stability, de Vries says, ''The instability seems to be a 
constant quality, although the words themselves are at 
first sight contradictory. I mean to convey the con- 
ception that the degree of instability remains unchanged 
during the successive generations." 

CE. elliptica is a very rare form both in the wild state 
and in cultivation. It is characterized by having narrow 
elliptical leaves and elliptical petals. 

ANALYTICAL TABLE OF SEEDLINGS (After de Vries) 

I. Leaves stalked. 

A. Leaves of the same breadth or 
broader. 1 
L Of the same breadth and shape, 
not to be distinguished as 
seedhngs. 

^ *' (than in Lamarkiana) " as also in the other analytical tables. 



Mutations 



69 



a. 
h. 

c. 

2. Broader, pointed, with many 

crumples. 

3. Broader, rounded at the tip 

with very deep crumples, 

edge incurved. 
a. 
b. 



1. (E. Lamarkiana. 

2. CE. brevistylis. 

3. (E. leptocarpa. 

4. (E. gigas. 



5. (E. lata. 

6. CE. semilata. 



B. Leaves narrower. 

1. Broadest in the middle. 

a. Very long with long stalks, 

with narrow veins, almost 
smooth. 

b. Small with broad leaf- stalk 

and broad, principal veins, 
very smooth, shiny dark 
green. 

2. Of equal breadth over the 

greater part of their length. 

a. Green. 

a. 1. Only slightly nar- 
rower, smooth with- 
out, or almost with- 
out crumples. 

a. 2. Very narrow with 

broad leaf-stalks 
and broad veins 
which often are red- 
dish ; wrinkled. 

b. Whitish. 

b. 1. Crumples many, 

pointed, narrowing 
off into the stalk. 
b. 2. Crumples few, nar- 
rowing off into the 
stalk, wavy, brittle, 
veins reddish. 



7. (E. elliptica. 



8. (E. scintillans. 



9. (E. Icevijolia. 



10. (E. oblonga. 



11. (E. albida. 



12. CE. rubrinervis. 



70 



Plant-Breeding 




Alutations 71 

6. 3, Crumples few, 
scarcely narrowing 
into the stalk, 
almost grasslike. 13. CE. sublinearis. 

]I. Leaves sessile, short and broad, 

almost heart-shaped, crumpled. 14. (E. nanella. 

How the mutants were produced in the garden. — Most 
of the types previously described were found growing 
wild near their parent species, (E. Lamarkiana. 

De Vries wished to determine whether these mutations 
could be produced from seed of (E. Lamarkiana planted in 
the garden (Fig. 21). Four series of experiments were 
performed, lasting through five to nine generations in 
which thousands of individuals were grown and studied. 
A description is here given of one of these experiments.^ 
The others were very similar. The pedigree culture began 
in 1886, when seed was planted in the garden from 
nine plants found growing wild. These nine plants 
constituted the first generation. The second generation 
flowered in 1889. This generation consisted of fifteen 
thousand seedlings of which ten were distinct mutations 
— five lata and five nanella. There were no intermediates. 

The third generation of ten thousand plants produced for 
the first time in pedigree cultures a plant of (E". ruhrinervis, 
along with three plants of CE. lata and three of (E. nanella. 

The fourth generation of fourteen thousand plants 
yielded a higher percentage of mutants. These were 
as follows : oblonga 176 ; lata 73 ; nanella 60 ; alhida 15 ; 
ruhrinervis 8 ; scintillans 1 ; and gigas 1 . 

1 De Vries, "Species and Variation, their Origin by Mutation," pp. 
549-575. 



72 



Plant-Breeding 



At this stage of the experiment, de Vries became expert 
in detecting variations at an early period. This accounts 
in part for the large number of mutants found in the 
fourth generation. By being able to pick out the mutat- 
ing forms at an early age, a much larger number of the 
diverging types could be obtained in proportion to the 
total number of individuals. 

De Vries gives the following table which represents 
graphically the results from eight generations of a mutating 
strain of (E. Lamarkiana : — 

Mutating Strains of CE. Lamarkiana 



Genera- 
tions 


GiGAS 


Albida 


Ob- 

LONGA 


RUBRI- 

NERVI8 


Lamark- 
iana 


Na- 
nella 


Lata 


SCINTIL- 
LAN8 


I 
II 










15000 


5 


5 




III 








1 


10000 


3 


3 




IV 


1 


15 


176 


8 


14000 


60 


73 


1 


V 




25 


136 


20 


8000 


49 


112 


6 


VI 




11 


29 


3 


1800 


9 


5 


1 


VII 






9 




3000 


11 






VIII 




5 


1 




1700 


21 


1 





De Vries^ laws of mutability of the evening-primroses. — 
de Vries deduced certain laws from the mutations in these 
(Enotheras. ''Obviously," he says, "they apply not only 
to our evening-primroses, but may be expected to be of 
general validity." 

These laws are as follows : — 

1. New elementary species appear suddenly, without 
intermediate steps. 



Mutations 73 

The ordinary conception had been that new types of 
plants had been produced by the slow and gradual piling 
up of small fluctuating variations. The experience with 
the primroses shows that new types are formed in much 
less time than it would take by the accumulation of small 
variations. It is remarkable that so many different new 
types of forms should have "been produced from the same 
parent and with no intermediates appearing. When 
(E. lata, which is a pistillate form, was crossed with 
(E. Lamarkiana, the progeny of the second generation 
segregated in mendelian proportion to the pure types of 
the parents, with no intermediates. This same absence 
of intermediacy is found when the progeny of the in- 
constant forms return each year to the parent species, 
Lamarkiana. 

2. New forms spring laterally from the main stem. 

This conception of the origin of new forms differs 
markedly from the Darwinian idea which assumes that 
species are slowly converted into others in the same 
direction and in the same degree. 

In such plants as draba or helianthemum, from which 
mutations have been known to arise, no center or "main 
stem" of mutation would have been known if it had not 
been seen to occur in pedigree-cultures. For instance, 
if gigas, ruhrinervis, and Lamarkiana had been found 
growing side by side in equal numbers in the wild state, 
it would have been impossible to tell which type had 
been the center of fluctuation. Many years of crossing, 
together with some vicinism which would probably have 
followed, would have been necessary to determine this. 
De Vries says, ''According to the current belief the con- 



74 Plant-Breeding 

version of a group of plants growing in any locality and 
flowering simultaneously would be restricted to one type. 
In my own experiments several new species arose from 
the parental form at once, giving a wide range of new forms 
at the same time and under same conditions." 

3. New elementary species attain their full constancy 
at once. 

'^Constancy is not the result of selection or of improve- 
ment. It is a quality of its own. It can neither be 
constrained by selection, if it is absent from the beginning, 
nor does it need any natural or artificial aid if it is present." 

No atavism was exhibited by the primrose mutations 
with the exceptions of CE. scintillans and (E. elUptica. 
These latter types reproduce themselves only in part in 
the offspring. De Vries says that the instability in these 
types seems to be as permanent a quality as the stability 
of the other forms. 

4. Some of the new strains are evidently elementary 
species, while others are to be considered as retrograde 
varieties. 

Such new forms as CE. gigas, ruhrinervis, ohlonga, and 
alhida may be called new elementary species. They are 
not differentiated from Lamarkiana by one or two main 
features, but they differ from it in nearly all organs, and 
hence may be considered new elementary species. The 
differences exist, not only in the foliage where they are 
most manifest, but in the stems, flowers, seeds, and in- 
deed, in many instances, to the minutest cell structure. 

CE. Icevifolia, CE. brevistylis, and CE. nanella, on the 
other hand, may be considered as retrograde varieties. 
They seem to differ from the parental form in but one 



Mutatidns 75 

character ; loevifolia is characterized by the loss of the 
crinkhng of the leaves ; hrevistylis, by the partial loss of 
the pistil ; and nanella, by the loss of stature. 

5. The new species are produced in a large number of 
individuals. 

It will be remembered that there were produced a 
large number of similar mutants in the same year, and 
also that the same mutations were produced in successive 
generations. 

There is obviously some cause for the production of 
these mutations. Whatever the exciting cause may be, 
the different mutants are not affected in the same way. 
Ohlonga, nanella, and lata are frequently produced, while 
gigas, rubrinervis, and scintillans are more rare. It has 
been found through later studies by Gates, Davis, Shull, 
and others that some of the types formerly thought by 
de Vries and others to be mutations are hybrids. 

It was found also that when the mutants were crossed 
together, types were found in the progeny which were 
the same as produced by (E". Lamarkiana itself. For 
example, (E. rubrinervis was observed by de Vries 
to arise in the hybrid progeny of (E. lata x nanella; 
(E. lata X brevistylis; CE. nanella x brevistylis ; and (E. 
scintillans X nanella. 

In nature, repeated mutations are probably of far more 
importance than isolated ones. The competition of 
plants is so great that the chances of the survival of one 
divergent individual are much less than as if these mutants 
were repeatedly produced in considerable quantity. 

6. Mutabihty is distinct from fluctuating variability. 
The foregoing evidence points to the fact that new 



76 Plant-Breeding 

forms are produced from quick sudden leaps. The new 
type is formed regardless of fluctuating variability, but 
the new form becomes a center of fluctuating variability 
similar to that around the parental form. 

7. The mutations take place in nearly all directions. 

De Vries says, ''Some of my new types are stouter and 
others weaker than their parents, as shown by gigas and 
albida. Some have broader leaves and some narrower 
(lata and ohlonga). Some have larger flowers (gigas) or 
deeper yellow ones (rubrinervis) or smaller blossoms 
(scintillans) or of a paler hue (albida). In some the 
capsules are longer (rubrinervis) or thicker (gigas) or 
more rounded (lata) or small (oblonga) or nearly destitute 
of seeds (brevistylis) . The unevenness of the surface of 
the leaves may increase as in lata or decrease as in Icevi- 
folia. The tendency to become annual prevails in ru- 
brinervis, but gigas tends to become biennial. Some are 
rich in pollen, while scintillans is poor. Some have large 
seeds, others small. Lata has become pistillate, while 
brevistylis has nearly lost the faculty to produce seeds. 
Some undescribed forms were quite sterile, and some I 
observed which produced no flowers at all." 

Examples of mutations. Shirley poppy. — Lock cites ^ 
the Shirley poppy as a mutation from the wild field poppy 
(Papaver Rhoeas) so common in England. It was first 
noticed in 1880 by the Rev. W. Wilks, Vicar of Shirley, 
near Croydon, England, in a patch of the wild forms 
growing in a waste corner of his garden. There suddenly 
appeared a solitary flower showing a very narrow border 

^ " Recent Progress in the Study of Variation, Heredity, and Evolu- 
tion," p. 133. 



Mutations 77 

of white. The seeds from this plant were saved and 
sown the next year. From this progeny of two hundred 
plants, four or five individuals appeared which showed 
the same diverging characteristics. 

''From these, by further horticultural processes, the 
strain of Shirley poppies originated." Lock remarks, 
in passing, that if the original plant had been self-pol- 
linated, a much larger proportion of the new type might 
have been expected to appear in the next generation. 

Cupid sweet pea. — Another example of a mutation is 
found in the case of the Cupid sweet pea (Fig. 22) . Until 
about fifteen years ago the only sweet peas known were 
the tall, climbing sorts, which grew to a height of 
three to six feet, depending on the richness of the soil. 
At this time, there was found in the seed trial grounds of 
Morse & Company of California, a small dwarf sweet 
pea plant only about six/ or eight inches high. This was 
growing in a row of the Emily Henderson variety, one of 
the ordinary tall sorts from which it evidently sprang. 
Seed of this dwarf plant was saved and grown and it was 
found to reproduce plants of the same dwarf character. 
The variety was designated ''The Cupid," under which 
name it was introduced to the seed trade and distributed 
over the world. The Cupid differed from other sweet 
peas not only in height, but in its closely set leaves and 
general habit of growth. Indeed, it is as distinct from 
other sweet peas as are distinct species of plants in 
nature. 

It has been found that this dwarf Cupid sweet pea 
mendelized with the tall ordinary sorts and appears as 
recessive. 



78 



Plant-Breeding 




Fig, 



22. _ Cupid sweet peas. (Photo by Beal.) 



Mutations 79 

Frequency of occurrence of mutations. — In general, it 
may be said that the occurrence of mutations is rare.^ 

In order to obtain a clear understanding of this subject, 
it may be divided into four sections : — 

1. Spontaneous occurrence of new varieties in the wild 
state. 

2. Spontaneous occurrence of new species in the wild 
state. 

3. Spontaneous occurrence of new varieties under 
cultivation. 

4. Spontaneous occurrence of new species under 
cultivation. 

The term "variety" as here used carries the meaning 
given by de Vries, — that of a group of plants differing 
from others in one systematic character. 

Spontaneous occurrence of new varieties in the wild 
state? — New varieties of plants are seen to occur rather 
rarely in the wild state. This may be due to two causes : 
(1) A lack of critical examination of wild plants for such 
spontaneous mutation ; and (2) if these mutations do 
occur, they are likely to meet premature death because 
of the severe competition to which all wild forms are 
subjected. 

As our wild plants are being studied more critically, 
it is being found that they do produce a much larger 
number of new varieties than was formerly supposed. 

In the case of the peloric toad-flax, which has been 
studied carefully by de Vries, the mutations are so numer- 

1 De Vries, p. 191. 

2 De Vries, "Species and Varieties, their Origin by Mutation," 
chapter on the Origin of Wild Species and Varieties, p. 576. 



80 Plant-Breeding 

ous that they seem to be quite regular. The peloric 
type is known to have originated from the ordinary type 
at different times and in different countries, under more 
or less divergent conditions. 

White varieties of many species of bluebells, gentians, 
and nearly all of the berry-bearing species in the large 
heather family are quite common. The same is true of 
the white flowers of Brunella vulgaris, Ononis repens, and 
Thymus vulgaris. 

Sponta7ieous occurrence of new elementary species in the 
wild state. — It will be remembered that new elementary 
species of the (Enothera were found to occur in the wild 
state before any attempt was made to study them under 
cultivation. It is difficult to say how frequently these 
mutations occurred in the wild because unquestionably 
most of them were destroyed prematurely, from the com- 
petition of other plants. 

The occurrence of new elementary species in the wild 
state seems to be much more rare than the occurrence of 
new varieties. This is natural, for, of course, elementary 
species present greater differences from the parental 
forms than do varieties. 

The spontaneous origin of the new elementary species, 
Capsella Heegeri, in 1897, has never been observed to have 
been repeated since that time.^ This new form of shep- 
herd's purse originated in the market-place near Landau, 
in Germany. 

Spontaneous occurrence of new elementary species and 
varieties under cultivation. — Whenever new forms occur 
spontaneously under cultivation, it should first be deter- 

1 De Vries, " Species and Varieties, their Origin by Mutation," p. 582. 



Mutations 



81 



mined whether they are the product of pure lines or not. 
If they come from pure lines, in all probability they are 
mutations ; if not, the new forms maybe a result of hybridi- 
zation, which may have taken place immediately preced- 
ing the appearance of the anomaly or at a considerable 
time previous to its appearance. 

New varieties and elementary species are seen to occur 
more often under cultivation for three reasons : — 

1. When new forms do occur, they are more Hkely to be 
seen. 

2. Because of the relative lack of competition and hence 
a better opportunity for preservation. 

3. The transfer of plants from the wild to the cultivated 
state has a tendency to break the type and cause spon- 
taneous new forms to ap- 
pear. For this reason, 
we may expect a more 
frequent occurrence of 
mutations under culti- 
vation. 

It is commonly ob- 
served among gardeners 
that so-called "sports" 
are of very common oc- 
currence. Some of these 
are monstrosities which 
are not inherited, but 
many of them are mu- 
tations and are inherited 
true to type. The occurrence of double-flowered types 
as mutations is common. 

G 







Fig. 23. — A, B, Linaria vulgaris; C, 
D, peloric flowers. 



82 



Plant-Breeding 




Fig. 24. — Linaria vulgaris peloria. A riclily branched stem of a plant 
of the second generation. Raised in 1898 from seed of the first 
generation of 1897, and photographed in August, 1900. All flowers 
are peloric. 



Mutations 



83 



Many mutations among cultivated plants are the result 
of continued selection for a period of years. This selection 
assists in breaking the type and thus permits the mutation 
to occur, and after the mutation has appeared, constant 
selection is not necessary to keep the new variety pure. 

It has been stated that the peloric type of toad-flax 
is of frequent occurrence in the wild state (Figs. 23 and 
24). De Vries found its appearance even more common 
under cultivation than when growing wild. He planted 
the seed of two toad-flax plants, one of which contained 
a single peloric flower. Eighteen hundred plants were 
obtained, of which seventeen, or nearly one per cent, 
were wholly peloric. 

The snapdragon {Antirrhinum majus) is also known to 
produce peloric flowers from time to time as mutations 
(Fig. 25). Pelorics occur sometimes in Linaria dalmatica 
and other species of Linaria; in fox-glove {Digitalis pur- 





FiG. 25. — Antirrhinum majus: A, peloric flower from the middle of an 
otherwise normal raceme ; B, normal flower of the same spike. 



84 Plant-Breeding 

purea), and in gloxinia. Many other instances of peloric 
flowers are on record, which indicates that pelorism as a 
mutation is frequent. 

Experimental study of the origin of mutations. — De Vries 
has conducted a series of experiments for the purpose of 
observing the origin of mutations, if any should occur. 
One of the plants chosen for these studies was the peloric 
toad-flax (Linaria vulgaris peloria). The most accurate 
laboratory methods were applied. The plants were 
carefully isolated in his garden. 

The reason for this choice of the peloric toad-flax lay 
in the fact that this form is known to have originated 
from the ordinary type at different times and in different 
countries under more or less divergent conditions. The 
ordinary toad-flax bears exceedingly unsymmetrical 
flowers. (See Fig. 23, A.) But symmetrical flowers are 
not uncommon in such plants as the toad-flax and snap- 
dragon, which have similar types of flowers. In these 
experiments, de Vries sought to observe the birth of this 
anomaly in his pedigree cultures. 

The experiments were begun in 1886 with normal 
plants ; a few peloric flowers were produced, however, 
which is not an uncommon occurrence among plants of 
this genus. Throughout the next few generations, 
nothing more than the normal number of peloric flowers 
were produced. 

In the third generation, among the many thousands of 
flowers there occurred one having five spurs. This was 
inbred by hand and produced a considerable quantity of 
seed. All other seed was discarded and this plant now 
became the parent of all future plants. 



Mutations 85 

The next (fourth) generation contained about twenty 
plants having only one peloric flower among them. The 
plant bearing this flower, and one other plant, were saved 
and all others discarded. These two were bred together 
and produced a considerable quantity of seed. 

In the next year (1894) fifty plants were in flower. 
Eleven of these were found to bear the normal number 
of peloric flowers. In addition to these eleven, there was 
found one plant which bore peloric flowers only. This 
was a mutation. Its appearance had been observed. It 
was found to breed true in future generations. 

In regard to the production of this mutation, de Vries 
says, '^Here we have the first experimental mutation of 
a normal into a peloric race. The facts were clear and 
simple : First, the ancestry was known for over a period 
of four generations. This ancestry was quite constant 
as to the peloric peculiarity remaining true to the wild 
type as it occurs everywhere in any country and showing 
in no respect any tendency to the production of a new 
variety. 

''Second, the mutation took place at once. It was a 
sudden leap from the normal plants with very rare peloric 
flowers to a type exclusively peloric. The parents them- 
selves had borne thousands of flowers during two sum- 
mers, and these were inspected nearly every day in the 
hope of finding some peloric and of saving their seed 
separately. Only one such flower was seen. There was 
no visible preparation for this sudden leap. 

''This leap, on the other hand, was full and complete. 
No reminiscence of the former condition remained. Not 
a single flower on the mutated plant reverted to the 



86 



Plant-Breeding 



previous type. The whole plant departed absolutely 
from the old type of its progenitors." 

What is true of the toad-flax is also true of the snap- 
dragon and other unsymmetrical flowers — the production 
of peloric flowers by mutation. 





Fig. 26. — Chrysanthemum segetum plenum. One of the six inflorescences 
which in 1899 first exhibited true "doubling." The figure represents 
the parent plant of the " double " variety. 

Experiments in the production of double flowers (Figs. 26- 
29) . — De Vries performed a series of experiments with the 
corn marigold {Chrysantheinam segetum) with the object 
of the production of double flowers. This plant has never 
been known to produce double flowers. The cultivated 
variety {grandiflorum) was found to be more stable and 
was used as a basis of the experiments. This cultivated 



Mutations 



87 



form has on the average twenty-one petals on each flower. 
In the population of the next generation there appeared 
one plant having twenty-one petals, but on one of its 
secondary heads twenty-two petals were found. This 
had never been observed before. This plant was the 




Fig. 27. — Chrysanthemum inodorum plenissimum : A, inflorescence with 
central disk of tube florets (fertile) ; B, with scattered tongue florets 
in the disk {ha,\i fertile) ; C, highest degree of " doubling " (sterile). 

beginning of what developed later into the desired muta- 
tion. 

This plant produced the next year (1897) plants having 
thirty-four rays to the head. Next year (1898) this was 
increased to forty-eight; next year (1899) to sixty-six. 



88 



Plant-Breeding 



During this time the means of the different generations 
were gradually increasing. So far there was observed a 

12 15 18 ?l 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99l02 




J^JL 



1897. 



1898. 



/-\ 




A A ^ 



1899. 




1900. 



M 



12 15 18 21 24 27 30 33 36 39 42 45 18 51 54 5' 60 63 66 69 72 75 78 61 84 87 90 93 96 99 102 



Fig, 28. — Ancestral generations of Chrysanthemum segetum plenum. 
Curves of the number of rays in the terminal inflorescence in the 
several individuals of the generations of 1897—1900. 



rapid increase in number of petals, but no indication of 
doubling. 

But this character soon appeared ; three secondary 
heads on one plant in the fall of 1899 showed a few ray- 



Mutations 



89 



florets scattered over the disk. An indication of the 
mutation was now seen. 

The next year, 1900, the highest number of rays arose 
to one hundred, and reached two hundred in 1901. These 




12 13 

A 



15 16 17 18 19 20 21 22 23 24 25 26 27 28 

B 



Fig. 29. — A, Chrysanthemum segetum; B, Chrysanthemum segetum 
grandiflorum (after purification). Curves of the races after isolation : 
A, curve of the 13-rayed race in 1894 ; B, curve of the 21 -rayed race 
in 1897. The ordinates give the number of individuals with like num- 
ber of ray-florets in the primary inflorescences of the individual plants. 
The number of ray-florets themselves is given below the abscissa. 



heads were completely double and the mutation had ap- 
peared, not quite as suddenly, perhaps, as with toad- 
flax, but nevertheless as surely. The new race was per- 
manent and constant. 

Complete doubleness caused sterility, so that the race 
had to be perpetuated from slightly inferior stock. 

Here, again, was the origin of a new mutation produced 
in control cultures by careful laboratory methods. 



90 Plant-Breeding 

What do new characters come from f — If mutations are 
the result of the appearance of new characters or the loss 
of old ones, where do these new characters come from 
and what causes the loss of existing ones ? The answer 
to this question would give us the keynote to the whole 
situation. If breeders possessed definite knowledge of 
the cause of mutations, they would then have within 
their control a kind of variation which could be made 
of tremendous economic importance. The causes are 
evidently from an internal origin. In all probability, 
many so-called mutations are due to hybrid origin and 
in the strictest sense are not mutations at all, even though 
they may be bred true. Much experimental evidence 
is necessary to determine with certainty their cause and 
control. 

Can mutations be produced artificially f — Must breeders 
passively wait for mutations to arise, or may they be 
produced artificially ? Many experiments are now being 
conducted to test this. So far, experiments do not seem 
to have led to any definite conclusion. 

Economic significance of mutations. — Agricultural and 
horticultural literature is full of accounts of the sudden 
origin, or at least the sudden finding, of exceptionally good 
plants which, when propagated, became the progenitors 
of new and valued races. So great is their number that 
not even an attempt to catalogue them can be made here. 

The pages of ^'Evolution of our Native Fruits" (Bailey) 
are filled with examples of mutation. The experience of 
plant-breeders and nurserymen show the origin of many 
varieties in this way. 

Many observing growers of cereals and other plants 



Mutations 91 

have originated varieties by finding occasionally unusually 
good plants and propagating from them. These excep- 
tional plants seem to bear no relationship to the others 
among which they are growing. Hybrid origin may 
account for certain of them and mutations for the others. 
Many of our well-known races of wheat have originated 
in this way. The Fultz wheat, which is a very popular 
and excellent race grown extensively in the Eastern States, 
was found in 1862 in a field of Lancaster Red by Mr. 
Abraham Fultz of Pennsylvania. Some beautiful heads 
of smoother wheat attracted his attention and they were 
saved and the seeds planted by themselves. These pro- 
duced the wheat later named the Fultz. The Tappa- 
hannock wheat, which, in 1872, was considered to be a 
valuable race, was found in 1854 by a Mr. Boughton, of 
Essex County, Virginia. The account of its discovery 
as given in the Report of the Department of Agriculture 
for 1872 is as follows: ''He noticed in his field a bunch 
of wheat of such growth as to attract his attention. . . . 
At harvest he found it to be a white wheat, at least two 
weeks earlier than the surrounding red wheat." Gold 
Coin Wheat, a seedling sport, differing from the hybrid 
Mediterranean in being bald and white, was found by 
Ira W. Green, of New York, in a field of that race and 
improved by selection. In the next five years the type 
was fixed and increased in yield about ten per cent. The 
American races, Wheatland Red, Pride Butte, and the 
well-known English races, Hopetown and Cavalier, were 
other accidental seedling races. 



CHAPTER VI 

THE PHILOSOPHY OF THE CROSSING OF 
PLANTS, CONSIDERED IN REFERENCE TO 
THEIR IMPROVEMENT UNDER CULTIVA- 
TION 

It is now understood that the specific forms or groups 
of plants have been determined largely by the survival 
of the fittest in a long and severe struggle for existence. 
The proof that this struggle everywhere exists becomes 
evident on a moment's reflection. We know that all 
organisms are eminently variable. In fact, no two plants 
or animals in the world are exactly alike. We also know 
that a very few of the whole number of seeds which are 
produced in any area ever grow into plants. If all the 
seeds produced by the elms upon Boston Common in 
any fruitful year were to grow into trees, the city would 
become a forest as a result. If all the seeds of the rarest 
orchids in our woods were to grow, in a few generations 
of plants even our farms would be overrun. If all the 
rabbits which are born were to reach old age, and all 
their offspring were to do the same, in less than ten years 
every vestige of herbage would be swept from the country, 
and our farms would become barren. 

The struggle for life. — There is, then, a wonderful 

92 



Hybridization 93 

latent potency in these species ; but the same may be said 
of every species of plant and animal, even of man himself. 
If one species of plant would overrun and usurp the land, 
if it increased to the fullest extent of its possibilities, 
what would be the result if each of the two thousand and 
sixty-one plants known to inhabit Middlesex County 
were to do the same ? And then fancy the result if each 
of the animals from rabbits and mice to frogs and leeches 
were to increase without check! The plagues of Egypt 
would be insignificant in the comparison ! 

Survival of the most fit. — The fact is, the world is not 
big enough to hold the possible first offspring of the 
plants and animals at this moment living upon it. 
Struggle for existence, then, is inevitable, and it must 
be severe. It follows as a necessity that those seeds 
grow or those plants live which are the best fitted to 
grow and live, or which are fortunate enough to find a 
congenial foothold. It would never appear, at first 
thought, that much depends on the accident of falling 
into a congenial place, or one unoccupied by other plants 
or animals; but, inasmuch as scores of plants are con- 
tending for every unoccupied place, it follows that every- 
where only the fittest can germinate or grow. In the 
greater number of cases, plants grow in a certain place 
because they are better fitted to grow there, to hold 
their own, than any other plants are; and the instances 
are rare in which a plant is so fortunate as to find an un- 
occupied place. We are likely to think that plants chance 
to grow where we find them, but the chance is determined 
by law, and, therefore, is not chance. 

Flexibility as an aid to survival. — Much of the capa- 



94 Plant-Breeding 

bility of a plant to persist under all this struggle depends, 
therefore, upon how much it varies ; for the more it varies, 
the more likely it is to find places of least struggle. It 
grows under various conditions, in the sun and shade, 
in sand and clay, by the sea-shore or upon the hills, in 
the humidity of the forest, or the aridity of the plain. 
In some directions it very likely finds less struggle than 
in others, and in these directions it may expand itself, 
multiply, and gradually die out in other directions ; so it 
happens that it tends to take on new forms or to undergo 
an evolution. In the meantime, all the intermediate 
forms, which are at best only indifferently adapted to 
their conditions, tend to disappear. In other words, 
gaps appear that we call '' missing links." The weak 
links break and fall away, and what was once a chain 
becomes a series of rings. So the '^missing links" are 
amongst the best proofs of evolution. 

Causes of variability. — The question now arises as to 
the cause of these numerous variations in animals and 
plants. Why are no two individuals in nature exactly 
alike? The question is exceedingly difficult to answer. 
It was once said that plants vary because it is their nature 
to vary ; that variation is a necessary function, as much 
as growth or fructification. This really removes the ques- 
tion beyond the reach of philosophy ; and direct observa- 
tion leads us to think that some variation, at least, is 
due to external circumstances. We are now looking for 
the cause of variation as a part of the scheme of evolu- 
tion ; and we are wondering whether the varied surround- 
ings, or, as Darwin puts it, '^ changed conditions of life," may 
not actually induce variability. This conclusion would 



Hybridization 95 

seem to follow from the fact of the severe and universal 
struggle in nature whereby plants are constantly forced 
into new and strange conditions. But there is un- 
doubtedly much variation which has sprung from more 
remote causes, one of which it is our purpose to discuss 
here. 

In the lowest plants and animals — which are merely 
single cells — the species multiplies by means of simple 
division or budding. One individual, of itself, becomes 
two, and the two are therefore recasts of the one. But, 
as organisms multiplied and conditions became more 
complex, that is, as struggle increased, there came a 
differentiation in the parts of the individual, so that one 
cell or one cluster of cells performed one labor and other 
cells performed other labor ; and this tendency resulted 
in the development of organs. Simple division, there- 
fore, might no longer reproduce the whole complex in- 
dividual ; and, as all organs are necessary to the existence 
of life, the organism may die if it is divided. 

Origin and function of sex. — Along with this specializa- 
tion came the differentiation into sex ; and sex clearly 
has two offices : to hand over the complex organization 
of the parent to the offspring and also to unite the essen- 
tial characters or tendencies of two beings into one. The 
second office is manifestly the greater, for, as it unites 
two organisms into one, it insures that the offspring is 
somewhat unlike either parent, and is therefore better 
fitted to seize upon any place or condition new to its 
kind. And as the generations increase, the tendency to 
variation in the offspring may be constantly greater be- 
cause of the impressions of the greater number of ancestors 



96 



Plant-Breeding 



transmitted to it. We have said that this office of sex to 
induce variation is more important than the mere fact of 
reproduction of a complex organization ; for it must be 
borne in mind that the complexity of organization is 
itself a variation and adaptation made necessary by the 
increasing struggle for existence. 




Fig. 30. — Extreme variability in the shape of the leaves of hybrid 
poppies. Second generation from a cross between the Bride variety 
of the Opium poppy and the Oriental poppy. 

If, therefore, the philosophy of sex is to promote variation 
by the union of different individuals, it must follow that 
the greatest variation must come from parents consider- 
ably unlike each other in their minor characters (Fig. 30) . 
Thus it comes that in-breeding tends to weaken a type 
and cross-breeding tends to strengthen it. At this point 
we meet that particular subject that we wish to discuss. 



Hybridization 97 

This preliminary discussion has been introduced because 
we can understand crossing only as we make it a part of 
the general philosophy of nature. There are the vaguest 
notions concerning the possibilities of crossing, some of 
which may be corrected by presenting the subject in its 
relations to the general aspects of the vegetable world. 
^^ Effects of crossing on the species. — We are now pre- 
pared to understand that crossing is good for the species, 
because it constantly revitalizes offspring with the strong- 
est traits of the parents, and ever presents new com- 
binations that enable the individuals to stand a better 
chance of securing a place in the polity of nature. The 
further discussions of the subject are such as have to do 
with the extent to which crossing is possible and advisable, 
and the general results of the operation. 

The limits of crossing. — If crossing is good for the 
species, which philosophy and direct experiment abun- 
dantly show, it is necessary at once to find out to what 
extent it can be carried. Does the good increase in pro- 
portion as the cross becomes more violent or as the parents 
are more and more unlike ? Or do we soon find a limit 
beyond which it is not profitable or even possible to go ? 
If great variability is good for the species in the struggle 
for existence, and if crossing induces variability because 
of the union of unlike individuals, it would seem to follow 
that the more unlike the parents, the greater will be 
the variation in offspring and the more the type will 
prosper; and, carrying this thought to its logical con- 
clusion, we shall expect to find that the most closely 
related plants would constantly tend to refuse to cross, 
because the offspring of them would be little variable 



98 Plant-Breeding 

and, therefore, little adapted to struggle for existence; 
while the most widely separated plants would constantly 
tend to cross more and more, because their offspring 
would present the greatest possible degree of differences. 

Swamping effects of inter-crossing. — Now, essentially 
this reason has been advanced to combat the evolution 
of plants and animals by means of natural selection ; and 
this proposition that inter-mixing must constantly tend 
to obliterate all differences between plants and to prevent 
the establishment of well-marked types, has been called 
the '^ swamping effects of inter-crossing." It is exceed- 
ingly important that we consider this question, for it 
really lies at the foundation of the improvement of cul- 
tivated plants by means of crossing, as well as the persist- 
ence and evolution of varieties and species under wholly 
natural conditions. 

What determines the limits of crossing f — We find, 
however, that distinct species, as a rule, refuse to cross ; 
and the first question which naturally arises is, what is 
the immediate cause of the refusal of plants to cross ? 
How does this refusal express itself ? It comes about 
in many ways. The commonest cause is the positive 
refusal of a plant to allow its ovule to be impregnated 
by the pollen of another plant. The pollen will not 
''take." For instance, if we apply the pollen of a Hub- 
bard squash to the flower of a common field pumpkin, 
there will be no result, — the fruit will not form. The 
same is true of the pear and the apple, the oat and the 
wheat, and most very unlike species. Or the refusal may 
come in the sterility of the cross or hybrid : the pollen 
may ''take" and seeds may be formed and the seeds 



•/ i 



Hybridization 99 

may grow, but the plants they produce may be wholly 
barren, sometimes even refusing to produce flowers 
as well as seeds, as in the instance of some hybrids be- 
tween the Wild Goose plum and the peach. Sometimes 
the refusal to cross is due to some difference in the time 
of blooming or some incompatibility in the structure of 
the flowers. But it is enough for our purpose to know 
that there are certain characters in widely dissimilar 
plants which prevent inter-crossing, and that these 
characters are just as closely and just as much influenced 
by change of environment and natural selection as are 
size, color, reproductiveness, and other characters. 

The limits of crossing tend to preserve the identity of 
species. — Here, then, is the sufficient answer to the prop- 
osition that inter-crossing must swamp all natural 
selection, and also the explanation of the varying and 
often restricted limits within which crossing is possible. 
That is, the checks to crossing have been deyeloped 
through the principle of universal variability and natural 
selection, as has been shown by Darwin and Wallace. 
Plants vary in their reproductive organs and powers, 
as they do in other directions ; and when such a varia- 
tion is useful it is perpetuated, and when hurtful it is 
lost. Suppose that a certain weU-marked individual of 
a species should find an unusually good place in nature, 
and it should multiply rapidly. Crosses would be made 
between its own offspring and perhaps between those 
offspring and itself in succeeding years; and it is fair 
to suppose that some of the crosses would be particularly 
well adapted to the conditions in which the parents 
grew, and these would constantly tend to perpetuate 



100 Plant-Breeding 

themselves, while less adaptive forms would tend similarly 
to disappear. Now the same thing would take place 
if this individual or its adaptive offspring were to cross 
with the main stock of the parent species ; for all the 
offspring of such a cross which is intermediate in character 
and therefore less adapted to the new conditions would 
tend to disappear, and the two types would, as a result, 
become more and more fixed and the tendency to cross 
would constantly decrease. 

The refusal to cross, the result of natural selection. — 
The refusal to cross, therefore, becomes a positive character 
of separation, and the '^missing links" that result from 
crossing are no more or no less inexplicable than the 
''missing links" due to simple selection; or, to state the 
case more accurately, natural selection weeds out the tend- 
ency to promiscuous crossing, when it is hurtful, in the 
same way that it weeds out any other injurious tendency. 
It makes no difference in what way this tendency ex- 
presses itself, whether in some constitutional refusal to 
cross, — if such exists, — or infertility of offspring, or 
in different times of blooming: all equally come under 
the power of natural selection. We are likely to look upon 
infertility as the absence of a character, a sort of negative 
feature which is somehow not the legitimate field of 
natural selection ; but such is not the case. We are 
perhaps led the more to this feeling because the word 
infertiUty is itself negative, and because we associate 
full productiveness with the positive attributes of plants. 
But loss of productiveness is surely no more a subject 
of wonder than loss of color or size, if there is some corre- 
sponding gain to be accomplished. In fact, we see, in 



Hybridization 101 

numerous plants which propagate usually by means of 
runners and suckers, a very low degree of productiveness, 
that is, infertility. 

For the production of useful hybrids, do not have the 
parents too diverse. — Now, if this reasoning is sound, 
it leads us to conclusions quite the reverse of those held 
by the advocates of the swamping effects of inter-crossing, 
and these conclusions are of the most vital importance 
to every man who tills the soil. The logical result is 
simply this : the best results of crossing are obtained, 
as a rule, when the cross is made between different in- 
dividuals of the same variety, or at farthest, between 
different individuals of the same species. In other words, 
crosses between species are very rarely useful in nature, 
and it follows that the more unlike the species, the less 
useful will be the hybrids. This is counter to the notions 
of most horticulturists, and, if true, must entirely over- 
throw our common thinking upon this subject. But we 
shall be able to show that observation and experiment 
lead to the same conclusion to which our philosophy 
has brought us. 

Function of the cross. — At this point, we must ask 
ourselves what we mean by ''best results." This phrase 
may be taken to refer to those plants that are best fitted to 
survive in the struggle for existence, those that are most 
vigorous or most productive or most hardy, or that 
possess any well-marked character or characters which 
distinguish them in virility from their fellows. We 
commonly associate the term more particularly with 
marked vigor and productiveness ; these are the char- 
acters most useful in nature and also in cultivation, the 



102 Plant-Breeding 

ones which we oftenest desire to obtain. Another type 
of variation that we constantly covet is something 
that we call a new character, which will lead to the 
production of a new cultural variety, and we are always 
looking to this as the legitimate result of crossing. We 
have forgotten — if, indeed, we ever knew — that the 
commoner, all-pervading, more important function of the 
cross is to introduce some new feature or power into the 
offspring, to improve or to perpetuate an existing variet}^, 
rather than to create a new one. Or, if a new one is 
created, it comes from the gradual passing of one into 
another, an inferior variety into a good one, a good one 
into a superlative one. So nature usually employs crossing 
in a process of slow or gradual improvement, one step 
leading to another, and not in any bold or sudden creation 
of new forms. And there is evidence to show that some- 
thing akin to this must be done to secure the best and 
most permanent results under cultivation. 

Rarity of natural hybrids. — Think of the great rarity 
of hybrids or pronounced crosses in nature. No doubt 
all the authentic cases on record could be entered into 
one or two volumes, but a list of all the individual plants 
of the world could not be compressed into ten thousand 
volumes. There are a few genera, in which the species 
are not well defined, or in which some character of in- 
florescence favors promiscuous crossing, in which hybrids 
are conspicuous ; but even here the number of individual 
hybrids is very small in comparison to the whole number 
of individuals. That is, the hybrids are rare, while the 
parents may be common. This is well illustrated even 
in the willows and the oaks, in which, perhaps, hybrids 



Hybridization 103 

are better known than in any other American plants. 
The great genus Carex, or sedge, which occurs in great 
numbers and many species in almost every locality in 
the United States, and in which the species are particularly 
adapted to inter-crossing by the character of their in- 
florescence, furnishes but few undoubted hybrids. Among 
one hundred and eighty-five species and prominent 
varieties inhabiting the Northeastern States, there are 
only about a score of hybrids recorded, and all of them are 
rare or local, some of them having been collected but 
once. Species of Carex of remarkable similarity may 
grow side by side for years, even inter-tangled in the 
same clump, and yet produce no hybrid. These examples 
show that nature avoids J iybr-idization, a conclusion at 
which we have already arrived from philosophical con- 
siderations. And we have reason to infer the same 
conclusion from the fact that flowers of different species 
are so constructed as not to invite inter-crossing. But, 
on the other hand, the fact that all higher plants habitually 
propagate by means of seeds, which is far the most ex- 
pensive to the plant of all methods of propagation, while 
at the same time most flowers are so constructed as to 
prevent self-fertilization, shows that some corresponding 
good must come from crossing within the limits of the 
species or variety ; and there are also philosophical reasons, 
as we have seen, that warrant this conclusion. 

Change of seed and crossing. — Bearing in mind these 
good influences of crossing, let us recall another series 
of facts following the simple change of seed. Almost 
every farmer and gardener at the present day feels that 
an occasional change of seed results in better crops, and 



104 Plant-Breeding 

there are definite records to show that such is often the 
case. In fact, much of the rapid improvement in fruits 
and vegetables in recent years is probably due to the 
practice of buying plants and seeds so largely of dealers, 
by means of which the stock is often changed. Even 
a slight change, as between farms or neighboring villages, 
sometimes produces marked results, such as more vigorous 
plants and often more fruitful ones. We must not sup- 
pose, however, that because a small change gives a good 
result, a violent or very pronounced change gives a better 
one. There are many facts on record to show that 
great changes often profoundly influence plants, and when 
such influence results in lessened vigor or lessened pro- 
ductiveness, we call it an injurious one. Now, this in- 
jurious influence may result even when all the condi- 
tions in the new place are favorable to the health and 
development of the plant ; it is an influence wholly in- 
dependent, as far as we can see, of any condition which 
interferes injuriously with the simple processes of growth. 
Seeds of a native physalis, or husk-tomato, were sent from 
Paraguay in 1889 by Dr. Thomas Morong, then traveling 
in that country. It was grown from cuttings in the house 
and out of doors, and for two generations it failed to set 
fruit, even though the flowers were hand pollinated ; yet the 
plants were healthy and grew vigorously. The third cut- 
ting-generation grown out of doors set freely. This is an 
instance of the fact that very great changes of conditions 
may injuriously affect the plant, and an equally good 
illustration of the power to overcome these conditions. 
Now there is great similarity between the effects of slight 
and violent changes of conditions and small and violent 



Hybridization 105 

degrees of crossing, as both Darwin and Wallace have 
pointed out, and it is pertinent to this discussion to 
endeavor to discover why this similarity exists. It is 
well proved that crossing is good for the resulting off- 
spring, because the difference between the parents carries 
over new combinations of characters, or at least new 
powers into the crosses. It is a process of revitaliza- 
tion, and the more different the stocks in desirable 
characters within the limits of the variety, the greater 
may be the revitalization ; and frequently the good is of a 
more positive kind, resulting in pronounced characters 
which may serve as the basis for new varieties. In the 
cross, therefore, a new combination of characters or a 
new power fit it to live better than its parents in the 
conditions under which they lived. 

Results from change of stock. — In the case of change of 
stock we find the reverse, which, however, amounts to the 
same thing, that the same characters or powers fit the plant 
to live better in conditions new to it than plants which 
have long lived in those conditions. In either case, the 
good comes from the fitting together of new characters or 
powers and new environments. Plants which live during 
many generations in one place become accustomed to the 
place, thoroughly fitted into its conditions, and are in 
what Spencer calls a state of equilibrium. When either 
plant or conditions change, new adjustments must take 
place; and the plant may find an opportunity to take 
advantage, to expand in some direction in which it has 
before been held back ; for plants always possess greater 
power than they are able to express. ^' These rhythmical 
actions or functions (of the organism)," writes Spencer, 



106 Plant-Breeding 

"and the various compound rhythms resulting from their 
combinations, are in such adjustment as to balance the 
actions to which the organism is subject. There is a 
constant or periodic genesis of forces which, in their kind, 
amounts, and directions, suffice to antagonize the forces 
which the organism has constantly or periodical!}^ to bear. 
If, then, there exists this state of moving equilibrium 
among a definite set of internal actions, exposed to a 
definite set of external actions, what must result if any of 
the external actions are changed ? Of course there is no 
longer an equilibrium. Some force which the organism 
habitualh^ generates is too great or too small to balance 
some incident force ; and there arises a residuary force 
exerted by the environment on the organism, or by the 
organism on the environment. This residuary' force, this 
unbalanced force, of necessity expends itself in producing 
some change of state in the organism." 

The good results, therefore, are processes of adaptation, 
and when adaptation is perfect or complete, the plant may 
have gained no permanent advantage over its former 
conditions, and new crossing or another change may be 
necessary ; yet there is often a permanent gain, as when a 
plant becomes visiblj^ modified by change to another cli- 
mate. Xow this adaptive change may express itself in 
two ways : either by some direct influence on the stature, 
vigor, or other general characters ; or directly on the 
reproductive powers, tiy which some new influence is 
carried to the offspring. If the direct influences become 
hereditary, as observations seem to show may sometimes 
occur, the two directions of modification may amount, 
ultimately, to the same thing. 



Hybridization 107 

For the purpose of this discussion it is enough to know 
that crossing within the variety and change of stock within 
ordinary bounds are beneficial, that the results in the two 
cases seem to flow from essentially the same causes, and 
that crossing and change of stock combined may give 
better results than either one alone ; and this benefit is 
expressed more in increased vigor and yield than in novel 
and striking variations. These processes are much more 
important than any mere groping after new variations, 
as we have already said, not only because they are surer, 
but because they are universal and necessary means of 
maintaining and improving both wild and cultivated 
plants. Even after one succeeds in securing and fixing 
the new variety, one must employ these means to a greater 
or less extent to maintain fertility and vigor, and to keep 
the variety true to its type. In the case of some garden 
crops, in which many seeds are produced in each fruit and 
in which the operation of pollination is easy, actual hand- 
crossing from new stock now and then may be found to be 
profitable. But in most cases the operation can be left 
to nature, if the new stock is planted among the old. 
Upon this point Darwin expressed himself as follows : 
''It is a common practice with horticulturists to obtain 
seeds from another place having a very different soil, so as 
to avoid raising plants for a long succession of generations 
under the same conditions ; but with all the species which 
freely inter-crossed by the aid of the insects or the ^vind, it 
would be an incomparably better plan to obtain seeds of 
the required variety, which had been raised for some 
generations under as different conditions as possible, and 
sow them in alternate rows with seeds matured in the old 



108 Plant-Breeding 

garden. The two stocks would then intercross, with a 
thorough blending of their whole organizations, and with 
no loss of purity to the variety, and this would yield far 
more favorable results than a mere change of seed." 

CROSSING FROM STANDPOINT OF PLANT IMPROVEMENT 

The making of crosses for man's use may have a very dif- 
ferent meaning from the effect of crossing upon the plant 
itself. Man removes from a plant by cultivation most of 
the factors which make for struggle and determines whether 
the plant shall survive or not. In making crosses or 
hybrids with a practical object in view, the welfare of the 
species is taken into account only sufficiently to insure 
vigorous plants particularly adapted to man's purposes. 

Understanding of terms. — At this point it is worth 
while to consider a few definitions. 

The Latin word hybrida, or ibrida, has been assumed to be 
derived from the Greek vfipL<;, an insult or outrage, and a 
hybrid has been supposed to be an outrage on nature, an un- 
natural product. The term hybrid is by many applied only 
to the offspring obtained by crossing two plants or animals 
sufficiently different to be considered by naturalists as 
distinct species, while the term cross is used to designate 
the offspring of two races or varieties of one species. A 
closer scrutiny of the facts, however, makes the term 
hybridism less isolated and more vague. The words 
species and genera, and still more sub-species and varieties, 
do not correspond with clearly marked botanical categories, 
and no exact line can be drawn between the various kinds 
of crossings from those between individuals apparently 
identical to those belonging to genera universally recog- 



Hybridization 109 

nized as distinct. It was formerly supposed that all 
hybrids were more or less sterile, in contradistinction to 
crosses, which were thought to be very fertile. It has 
been found, however, that many hybrids, in the narrow 
sense, are very fertile, and that some crosses are nearly 
sterile. Since it is impossible to indicate by any two words, 
such as hybrid or cross, the various degrees of difference 
of the forms crossed, the word hybrid is now generally 
used as a generic term to include all organisms arising 
from a cross of two forms noticeably different, whether the 
difference be great or slight. Adjectives are sometimes 
used to indicate the grade of the forms crossed, such as 
racial hybrids, bigeneric hybrids, and so forth. 

The offspring produced by the union of two plants 
identical in kind, but separated in descent by at least 
several seed generations, is often called a cross, cross- 
fertilized, or cross-bred plant, but it is not a hybrid, as 
the essential character of a hybrid is that it results from 
the union of plants differing more or less in kind, or, in 
other words, is the result of a union between different races, 
varieties, species, or genera. On the other hand, flowers 
impregnated with their own pollen, with the pollen of 
another flower on the same plant, or even pollen from 
another plant derived from the same original stock by 
cuttings or grafts, are said to be self-fertilized, and the 
offspring resulting from such unions are often termed self- 
fertilized plants. Strictly speaking, however, self- or close- 
fertilization is impregnation with pollen of the same flower. 
With such plants as tobacco and wheat, self-fertilization 
is the rule. In many cases, however, the flowers are so 
constructed that cross-fertilization is favored, as in corn 



110 Plant-Breeding 

and rye, and in some cases cross-fertilization is necessary, 
all possibility of self-pollinization being precluded, as in 
the case of hemp and other plants having the male and 
female flowers on separate individuals. 

History of plant hybrids. — Inasmuch as the sexuality of 
plants was unknown, or at least very imperfectly under- 
stood, prior to the last two centuries, while a knowledge 
of the sex distinction of animals dates from the dawn of 
human history, it is not surprising that while the hybridiz- 
ing of animals was well understood by the ancients, they 
did not know that crossing was possible with plants. 
Experimental proof of the sexuality of plants was pub- 
lished for the first time by Camerarius, December 28, 
1691, and only after this discovery was the function 
of pollen and its necessity for seed formation under- 
stood. 

The earliest recorded observation of a plant hybrid is by 
J. G. Gmelin toward the end of the seventeenth century ; 
the next is that of Thomas Fairchild, who in the second 
decade of the eighteenth century produced the cross 
which is still grown in literature under the name of 
''Fairchild's Sweet William." It was a cross between the 
carnation and sweet William. 

Linnaeus made many experiments in the cross-fertiliza- 
tion of plants and produced several hybrids, but Joseph 
Gottheb Kolreuter (1733-1806) laid the real foundation 
of our scientific knowledge of the subject. Later on, 
Thomas Andrew Knight, a celebrated English horticul- 
turist, devoted much successful labor to the improvement 
of fruit trees and vegetables by crossing. In the second 
quarter of the nineteenth century, C. F. Gartner made 



Hybridization 111 

and published the results of a number of experiments that 
have not been equaled by any other worker. 

What plants can be hybridized ? — It is a fact of prime 
importance that plants so different as to be classed by 
botanists in widely different families never yield offspring 
when crossed ; for example, it is impossible successfully 
to cross Indian corn and lilies or the apple and the wal- 
nut. Usually plants diverse enough to be considered as 
belonging to clearly distinct genera, even though of the 
same natural family, are perfectly sterile when crossed ; 
for example, Indian corn yields no offspring when cross- 
pollinated with wheat, nor does wheat when crossed with 
oats, although all belong to the great family of grasses.' 
Plants belonging to the different cultivated races or to 
natural varieties of the same species are almost invariably 
fertile when crossed. Indeed, as will be shown later, they 
are sometimes more fertile when crossed with a related 
species than when fertilized with their own pollen. Dif- 
ferent species of plants closely enough related to be placed 
in the same genus by naturalists are very often, though by 
no means always, capable of being hybridized. 

Gartner found that '^one of the tobaccoes, Nicotiana 
acuminata, which is not a particularly distinct species, 
obstinately failed to fertilize or to be fertilized by no less 
than eight species of Nicotiana." Darwin states that ''in 
the same family there may be a genus, as Dianthus, in 
which very many species can most readily be crossed ; 
and another genus, as Silene, in which the m.ost persever- 
ing efforts have failed to produce, between extremely close 
species, a single hybrid." Again, there is considerable 
diversity in results in certain reciprocal crosses between 



i^ 



112 Plant-Breeding 

the same two species. "Mirabilis jalapa can easily be 
fertilized by the pollen of M. longiflora, and the hybrids 
thus produced are sufficiently fertile ; but Kolreuter tried 
more than two hundred times during eight following years 
to fertilize reciprocally M. longiflora with the pollen of 
M. jalapa and utterly failed/' as have also many other 
hybridizers. Frequently very closely related species 
absolutely refuse to cross. This is true of the pumpkin 
{Cucurhita Pepo) and squash (C. maxima). It is, never- 
theless, true that hosts of very distinct species hybridize 
readily, and a number of cases are known of species be- 
longing to different and quite distinct genera having 
hybridized, producing the so-called bigeneric hybrids. 
For example, wheat and rye, and wheat and barley, be- 
longing to closely related genera, cross with difficulty, and 
Luther Burbank is said to have succeeded in obtaining a 
hybrid of strawberry and raspberry. Bigeneric hybrids 
are many among the orchids, even though they are highly 
specialized plants ; and some trigeneric hybrids are known. 

Hybrids between plants belonging to different families 
are very rare. The results obtained by hosts of experi- 
menters and practical gardeners show conclusively that 
the greater part of closely related species can be readily 
crossed, while very distinct species, and species belonging 
to distinct genera, can be crossed in only comparatively 
few cases. It is impossible to predict what plants may or 
may not be hybridized. 

Vigor as a result of crossing. — Darwin was the first to 
show that crossing within the limits of the species or 
variety results in a constant revitalizing of the offspring, 
and that this is the particular ultimate function of crossing 



Hybridization 



113 



or cross-fertilization. Kolreuter, Sprengel, Knight, and 
others had observed many, if, indeed, not all, the facts 
obtained by Darwin ; but they had not generalized upon 
them broadly, and did not conceive the relation to the 
complex life of the vegetable world. Darwin's results 
are, concisely, these : self-fertilization tends to weaken the 
offspring (Fig. 31) ; crossing between different plants of the 




Fig. 31. — Inbred corn plants, showing lessened vigor of growth. 
(Adapted from Yearbook.) 



same variety gives a stronger and more productive offspring 
than arises from self-fertilization ; crossing between stocks 
of the same variety grown in different places or under 
different conditions gives better offspring than crossing 
between different plants grown in the same place or under 
similar conditions ; and his researches have also shown that, 
as a rule, flowers are so constructed as to favor cross- 



114 Plant-Breeding 

fertilization. In short, he found, as he expressed it, that 
'' nature abhors perpetual self-fertilization." Some of his 
particular results, although often quoted, will be useful in 
fixing these facts in our minds. 

Darwin's experiments with morning-glories. — Plants 
from crossed seeds of morning-glory exceeded in height 
those from self-fertilized seeds as 100 exceeds 76, in the 
first generation. Some flowers from these plants were 
self-pollinated and some were crossed, and in this second 
generation the crossed plants were to the uncrossed as 
100 is to 79 ; the operation was again repeated, and in the 
third generation, the plant having been grown in mid- 
winter, when none of them did well, 100 to 86 ; fifth 
generation, 100 to 75 ; sixth generation, 100 to 72 ; seventh 
generation, 100 to 81 ; eighth generation, 100 to 85 ; ninth 
generation, 100 to 79 ; tenth generation, 100 to 54. The 
average total gain in height of the crossed over the un- 
crossed was as 100 to 77, or about 30 per cent. There 
was a corresponding gain in fertihty, or the number of 
seeds and seed-pods produced. Yet, striking as the results 
are, they were produced by simple crossing between plants 
grown near together, and under what would ordinarily 
be called uniform conditions. In order to determine the 
influence of crossing with fresh stock, plants of the same 
variety were obtained from another garden and these 
were crossed with the ninth generation mentioned above. 
The offspring of this cross exceeded those of the other 
crossed plants as 100 exceeds 78, in height ; as 100 exceeds 
57, in the number of seed-pods ; and as 100 exceeds 51, 
in the weight of the seed-pods. In other words, crosses 
between fresh stock of the same variety were nearly 30 



Hybridization 115 

per cent more vigorous than crosses between plants grown 
side by side for some time and over 44 per cent more 
vigorous than plants from self-fertilized seeds. On the 
other hand, experiments showed that crosses between 
different flowers on the same plant gave actually poorer 
results than offspring of self-fertilized flowers. It is 
evident, from all of these figures, that nature desires 
crosses between plants, and, if possible, between plants 
grown under somewhat different conditions. All these 
results are exceedingly interesting and important ; and 
there is every reason to beUeve that, as a rule, similar 
results can be obtained with all plants. 

Darwin'' s results with other plants. — Darwin extended 
his investigation to many plants, only a few of which need 
be discussed here. Cabbage gave pronounced results. 
Crossed plants were to self-fertilized plants in weight as 
100 is to 37. A cross was now made between these crossed 
plants and a plant of the same variety from another 
garden, and the difference in weight of the resulting off- 
spring was the difference between 100 and 22, showing a 
gain of over 350 per cent, due to a cross with fresh stock. 
Crossed lettuce plants exceeded uncrossed in height as 
100 exceeds 82. Buckwheat gave an increase in weight 
of seeds as 100 to 82, and in height of plants as 100 to 69. 
Beets gave an increase in height represented by 100 to 87. 
Maize, when full grown, from crossed and uncrossed seeds, 
gave the difference in height between 100 and 91. Canary 
grass gave similar results. 

Increased vigor in other crosses. — Results as well 
marked as these have been secured on a large and what 
might be called a commercial scale. The first gen- 



116 Plant-Breeding 

eration was raised from seeds of known parentage, 
the flowers from which they came having been carefully 
poUinated by hand. In some instances the second genera- 
tions were grown from hand-crossed seeds, but in other 
cases the second generations were grown from seeds simply 
selected from the first-year patches. As the experiments 
have been made in the field and upon a somewhat exten- 
sive scale, it was not possible accurately to measure the 
plants and the fruits from individuals in all cases ; but the 
results have been so marked as to admit of no doubt as 
to their character. In 1889, several hand-crosses were 
made among egg-plants. The fruits matured, and the 
seeds from them were grown in 1890. Some two hundred 
plants were grown, and they were characterized through- 
out the season by great sturdiness and vigor of gro^vth. 
They grew more erect and taller than other plants near by 
gro^vn from commercial seeds. It was impossible to deter- 
mine productiveness, from the fact that the seasons were 
too short for egg-plants, and only the earliest flowers, in 
the large varieties, perfect their fruit, and the plant blooms 
continuously through the season. In order to determine 
how much a plant will bear, it must be gro^vn until it 
ceases to bloom. When frost came, httle difference could 
be seen in productiveness between these crossed plants 
and commercial plants. A dozen fruits were selected from 
various parts of the patch, and in 1891 about twenty-five 
hundred plants were grown from them. Again the plants 
were remarkably robust and healthy, with fine foliage, 
and they grew erect and tall, — an indication of vigor. 
They were also very productive ; but, as the cross had 
been made between unhke varieties, and the offspring 



Hybridization 



117 



was therefore unlike either parent, an accurate comparison 
could not be made. But they compared well with com- 
mercial egg-plants, and un- 
doubtedly they would have 
shown themselves to be 
more productive than com- 
mon stock could they have 
grown a month or six weeks 
longer. Professor Munson, 
of the Maine Experiment 
Station, grew some of this 
crossed stock in 1891, and 
found that it was better 
than any commercial stock 
in his gardens. 

In extended experiments 
in the crossing of pumpkins, 
squashes, and gourds, con- 
ducted several years, in- 
crease in productiveness 
due to crossing has been 
marked in many instances. 
Marked increase in produc- 
tiveness has been obtained 
from tomato crosses even 
when no other results of 
crossing could be seen. 

Three factors. — Attention 
has been called by WiUis to 

three factors in the gain resulting from cross-fertihzation, 
viz. (a) fertility of mother plant ; (b) vigor of offspring ; 




Fig. 32. — Hybrid walnut and 
parent.s : m, California black 
walnut {Juglans calif arnica), 
male parent; /, Eastern black 
walnut (./. nigra), female par- 
ent ; h, hybrid. Natural size. 
(After Bur bank.) 



118 Plant-Breeding 

and (c) fertility of offspring. The relative values of these 
factors varies with different plants. In the carnation, for 
instance, factor (a) of cross-fertilized plants was 9 per cent 
greater than in self -fertilized plants, (6) was 16 per cent 
greater, and (c) was 54 per cent greater ; in tobacco, 
factor (a) was 33 per cent less than in self-fertiHzed plants, 
but factor (h) was 28 per cent greater and factor (c) 3 per 
cent greater. Even when the fertility of the mother 
plant is greatly reduced by hybridizing with a distinct 
species and the hybrids themselves are sterile or very 
infertile, they nevertheless often show extraordinary vigor, 
that is, (b) is often greater in hybrids than in pure-bred 
plants, but factors (a) and (c) are usually less. In plant- 
breeding the importance of this increased vigor is very 
great (Figs. 32 and 33). 

The outright production of new varieties. — ^The reader is 
waiting for a discussion of the second of the great features 
of crossing, — the summary production of new varieties. 
This is the subject that is almost universally associated 
with crossing in the popular mind, and even among hor- 
ticulturists themselves. It is the commonest notion that 
the desirable characters of given parents can be definitely 
combined in a pronounced cross of hybrids. There are 
two or three philosophical reasons which somewhat oppose 
this doctrine, and which we will do well to consider at the 
outset. In the first place, nature is opposed to hybrids, 
for species have been bred away from each other in the 
ability to cross. If, therefore, there is no advantage for 
nature to hybridize, we may suppose that there would be 
little advantage for man to do so ; and there would be no 
advantage for man did he not place the plant under condi- 




Fig. 33. — A hybrid walnut {Jiiglans californica nigra), reaching double 
the height of ordinary trees. 



120 Plant-Breeding 

tions different from nature, or desires a different set of 
char^^cters. We have seen that nature's chief barriers to 
hybridization are total refusal of many species to unite, 
and entire or comparative seedlessness of offspring. 

The notion is somewhat firmly rooted in the popular 
mind that new varieties can be produced with the greatest 
ease by crossing parents of given attributes. There is 
something captivating about the notion. It smacks of a 
somewhat magic power that man evokes as he passes his 
wand over the untamed forces of nature. But the wand 
is often a gilded stick, and is likely to serve no better 
purpose than the drum major's pretentious baton ! 

Let it be said further that crossing alone can accompHsh 
comparatively Httle. The chief power in the evolution or 
progression of plants appears to be selection, or, as Darwin 
puts it, the law of ^^preservation of favorable individual 
differences and variations, and the destruction of those 
which are injurious." Selection is the force which aug- 
ments, develops, and fixes types. Man must not only 
practice a judicious selection of parents from which the 
cross is to come, which is in reality but the exercise of a 
choice, but he must constantly select the best from among 
the crosses, in order to maintain a high degree of usefulness 
and to make anj^ advancement ; and it sometimes happens 
that the selection is much more important to the cultivator 
than the crossing. 

Further discussion of this subject naturally falls under 
two heads : the improvement of existing types or varieties 
by means of crossing, and the summary production of new 
varieties. As already stated, the former office is the more 
important, and the proposition is easy of proof. It is 



Hybridization 121 

the chief use which nature makes of crossing, to strengthen 
the type. 

How to overcome antipathy to crossing. — We can over- 
come the refusal to cross in many cases by bringing the 
plant under cultivation; for the character of the species 
becomes so changed by the wholly new conditions that its 
former antipathies may be overpowered. Yet, it is doubt- 
ful whether such a plant will ever acquire a complete willing- 
ness to cross. In like manner we can overcome in a meas- 
ure the comparative seedlessness of hybrids, but it is very 
doubtful whether we can ever make such hybrids com- 
pletely fruitful. 

It is evident that species which have been differentiated 
or bred away from each other in a given locality will have 
more opposed quaUties or powers than similar species 
which have arisen quite independently in places remote 
from each other. In the one case the species have Ukely 
struggled with each other until each one has attained to a 
degree of divergence which allows it to persist ; while in 
the other case, there has been no struggle between species, 
but similar conditions have brought about similar results. 
These similar species which appear independentl}^ of each 
other in different places are called representative species. 
Islands remote from each other but similarly situated with 
reference to climate very often contain representative 
species ; and the same may be said of other regions much 
like each other, as eastern North America and Japan. 
Now, it follows that, if representative species are less 
opposed than others, they are more Hkely to hybridize with 
good results ; and this fact is remarkably well illustrated in 
the Kieffer and allied pears, which are hybrids between 



122 Plant-Breeding 

representative species of Europe and Japan ; and the 
same may be found to be true of the common European 
applp and the wild crab of the Mississippi Valley. 
Various crabs of the Soulard type, which were once 
thought to constitute a distinct species, appear upon 
further study to be hybrids. We will also recall that 
the hybrid grapes which have so far proved most 
valuable are those obtained by Rogers between the 
American Vitis Labrusca and the European wine grape, 
Vitis vinifera; and that the attempts of Haskell and 
others to hybridize associated species of native grapes have 
given, at best, only indifferent results. To these good 
results from hybrids and fruit trees and vines, we shall 
revert presently. 

Variability of hybrids. — Another theoretical point 
which is borne out by practice is the conclusion that, 
because of the great differences and lack of affinity between 
parents, pronounced hybrid offsprings are unstable. This 
is one of the greatest difficulties in the way of the summary 
production of new varieties by means of hybridization. 
It would appear, also, that, because of the unlikeness of 
parents, hybrid offspring must be exceedingly variable ; 
but, as a matter of fact, in many instances the parents are 
so pronouncedly different that the hybrids represent a 
distinct type by themselves, or else they approach very 
nearly to the characters of one of the parents. There are, 
to be sure, many examples of exceedingly variable hybrid 
offspring, but they are usually the offspring of variable 
parents (Fig. 34) . In other words, variability in offspring 
appears to follow rather as a result of variability in parents 
than as a result of mere unhkeness of characters. But 



Hybridization 



123 



the instability of hybrid offspring when propagated by 
seed is notorious. We shall see the reasons for this later 
when discussing mendelism. Wallace writes that ''the 
effect of occasional crosses often results in a great amount 
of variability, but it also leads to instability of character, 
and is therefore very little employed in the production of 
fixed and well-marked races." We may remark again that, 
because of the unequal and unknown powers of the parents, 
we can never predict what characters will appear in the 




Fig. 34. — Variation in hybrid pineapples. 



hybrids, although we are now beginning to understand 
the reasons and to have rather definite expectations as 
to probabilities. This fact is well expressed by Lindley a 
half century ago, in the phrase, ''Hybridizing is a game 
of chance played between man and plants." 

Characteristics of crosses. — Bearing these fundamental 
propositions in mind, let us pursue the subject somewhat 
in detail. We shall find that the characters of hybrids, 
as compared with the characters of simple crosses between 
stocks of the same variety, are ambiguous, negative, and 



124 Plant- Breeding 

often prejudicial. Focke lays down the five following 
propositions concerning the character of hybrid offspring : 

1. ''All individuals which have come from the crossing 
of two pure species or races, when produced and grown 
under like conditions, are usually exactly like each other, 
or at least scarcely more different from each other than 
plants of the same species are." This proposition, al- 
though perhaps true in the main, appears to be too broadly 
and positively stated. 

2. ''The characters of hybrids may be different from 
the characters of the parents. The hybrids differ most in 
size and vigor and in their sexual powers. 

3. "Hybrids are distinguished from their parents by 
their powers of vegetation or growth. Hybrids between 
very different species are often weak, especially when 
young, so that it is difficult to raise them. On the other 
hand, crossbreds are, as a rule, uncommonly vigorous ; 
they are distinguished mostly in size, rapidity of growth, 
early flowering, productiveness, longer life, stronger repro- 
ductive power, unusual size of some special organs, and 
similar characteristics. 

4. "Hybrids produce a less amount of pollen and fewer 
seeds than their parents, and they often produce none. 
In cross-breeds this weakening of the reproductive powers 
does not occur. The flowers of sterile or nearly sterile 
hybrids usually remain fresh a long time. 

5. "Malformations and odd forms are likely to appear 
in hybrids, especially in the flowers." 

Some of the relations between hybridization and cross- 
ing within narrow limits are stated as follows by Darwin : 
" It is an extraordinary fact that with many species flowers 



Hybridization 125 

fertilized with their own pollen are either absolutely or in 
some degree sterile ; if fertilized with pollen from another 
flower on the same plant, they are sometimes, though 
rarely, a little more fertile ; if fertilized with pollen from 
another individual or variety of the same species, they 
are fully fertile ; but if with pollen from a distinct species, 
the}^ are sterile in all possible degrees, until utter sterility 
is reached. We thus have a long series with absolute 
sterility at the two ends; at one end due to the sexual 
elements not having been sufficiently differentiated, and 
at the other end to their having been differentiated in too 
great a degree, or in some peculiar manner," 

Difficulties in making successful crosses. — The diffi- 
culties in the way of successful results through hybridiza- 
tion are, therefore, these : the difficulty of effecting the 
cross, infertility, instability, variability, and often weak- 
ness and m.onstrosity of the hybrids ; and the general 
impossibility in most cases of predicting results. The 
advantage to be derived from a successful hybridization 
is the securing of a new variety which shall combine in 
some measure the most desirable features of both parents ; 
and this advantage is often of so great moment that it is 
worth while to make repeated efforts and to overlook 
numerous failures. 

Hybridization and asexual propagation. — Among the 
various characters of hybrid offspring, probably the most 
prejudicial one is their instability, their tendency to vary 
into new forms or to return to one or the other parent 
in succeeding generations. At the outset, we notice that 
this discouraging feature is manifested chiefly through 
the fact of seed-reproduction, and we thereby come 



126 Plant-Breeding 

upon what is perhaps the most important practical con- 
sideration in hybridization, — the fact that the greater 
number of the best hybrids in cultivation are increased 
by bud-propagation, as cuttings, layers, suckers, buds, or 
grafts. In fact, there are very few examples in this country 
of good undoubted hybrids which are propagated with 
practical certainty by means of seeds. The genera in 
which the hybrids are most common are those in which 
bud-propagation is the rule ; as begonia, pelargonium, 
orchids, gladiolus, rhododendron, roses, cannas, and the 
fruits. This simply means that it is difficult to fix hybrids 
so that they will come ^'true to seed," and makes apparent 
the fact that if we desire named hybrids, we must expect 
to propagate them by means of buds. 

This point appears to have been overlooked by those 
who contend that hybridization must necessarily swamp 
all results of natural selection ; for, as comparatively 
few plants propagate habitually by means of buds, 
whatever hybrids might have appeared would have been 
speedily lost, and all the more because, by the terms of 
their reasoning, the hybrids would cross with other and 
dissimilar forms, and therefore lose their identity as 
intermediates. Or, starting ^vith the assumption that 
hybrids are intermediates, and would therefore obliterate 
specific types, we must conclude that they should have 
some marked degree of stability if they are to swamp or 
obliterate the characters of species ; but, as all hybrids 
tend to break up when propagated by seeds, it must follow 
that bud-propagation would become more and more 
common, and this is associated in nature with decreased 
seed-production. Now, seed-production is the legitimate 



Hybridization 127 

function of flowers; and we must concede that, as seed- 
production decreased, floriferousness must have decreased ; 
and that, therefore, pronounced inter-crossing would have 
obliterated the very organs upon which it depends, or have 
destroyed itself! 

In-breeding. — But we may be met with objection that 
there is no inherent reason why hybrids should not become 
stable through seed-production by in-breeding, and we 
might be cited to the opinion of Darwin and others that 
in-breeding tends to fix any variety, whether it originates 
by crossing or other means. And it is a fact that in- 
breeding tends to fix varieties within certain limits, but 
those limits are often overpassed in the case of very pro- 
nounced crosses, whether cross-breeds or true hybrids. 
And if it is true, as all observation and experiments show, 
that sexual or reproductive powers of crosses are weakened 
as the cross becomes more violent, we shall expect less and 
less possibilit}^ of successful in-breeding ; for in-breeding 
without disastrous results is possible only with compara- 
tively strong reproductive powers. As a matter of fact, 
it is found in practice that it is exceedingly difficult to fix 
pronounced hybrids by means of in-breeding. It some- 
times happens, also, that the hybrid individual that we 
wish to perpetuate ma}' be infertile with itself, as has been 
often found in the case of squashes. It is often advised 
that we cross the hybrid individual which we wish to fix 
with another like individual, or \\dth one of its parents. 
These results are often successful, but oftener they are not. 
In the first place, it often happens that the hybrid individ- 
uals maj' be so diverse that no two of them are alike ; 
this has been the experience in many cases. And, again 



128 Plant-Breeding 

crossing with a parent may draw the hybrid back again to 
the parent form. So long ago as last century Kolreuter 
proved this fact with Nicotiana and Dianthus. A hybrid 
between Nicotiana rustica and N. paniculata was crossed 
with N. paniculata until it was indistinguishable from it ; 
and it was then crossed with N. rustica until it became 
indistinguishable from that parent. Yet there is no other 
way of fixing a hybrid to be propagated by seeds than 
by in-breeding, and by constant attention to selection. 
Fortunately, it occasionally happens that a hybrid is 
stable, and therefore needs no fixing. 

Experience with egg-plants and squashes. — Offspring of 
egg-plant crosses were grown in 1890, and upon some of 
the most promising plants some flowers were self -pollinated. 
But these self-pollinated seeds gave just as variable offspring 
in 1891 as those selected almost at random from the patch ; 
and what was worse, none of them reproduced the parents, 
or ''came true to seed," and all further motive for in- 
breeding was gone. ''My labor, therefore, amounted to 
nothing more than my own edification. M}^ experience 
in crossing pumpkins and squashes has now extended 
through many years ; and, although I have obtained about 
one thousand types not named or described, I have not 
yet succeeded in fixing one. The difficulty here is an 
aggravated one, however. The species are so exceedingly 
variable that all the hybrid individuals may be unlike, so 
that there can be no crossing between identical stocks ; 
and, if in-breeding is attempted, it may be found that the 
flowers will not in-breed. And the refusal to in-breed is 
all the more strange because the sexes are separated in 
different flowers on the plant. In other words, in my 



Hybridization 



129 



experience, it is very difficult to get good seeds from 
squashes fertilized by a flower upon the same vine. 
The squashes may grow normally to full maturity but be 
entirely hollow, or contain only empty seeds. In some 
instances the seeds may appear to be good, but may 
refuse to grow under the best conditions. Finally, a 




Fig. 35. — Variation in hybrid squashes. 

small number of flowers may give good seeds. I have 
many times observed this refusal of squashes (Cucurhita 
Pepo) to in-breed. It was first brought to my attention 
through efforts to fix certain types into varieties. The 
figures of the season's tests will sufficiently indicate the 
character of the problem. In 1890, one hundred and 



130 Plant-Breeding 

eighty-five squash flowers were carefully pollinated with 
staminate flowers taken from the same vine that bore the 
pistillate flowers. Only twenty-two of these produced 
fruit, and of those only seven, or less than one-third, bore 
good seeds, and in some of these the seeds were few. Now, 
these twenty-two fruits represented as many different 
varieties, so that the inability to set fruit with pollen, 
from the same vine is not a peculiarity of a particular 
variety. The records of the seeds of the seven fruits in 
1891 are as follows : — ■ 

''Fruit No. 1. Four vines were obtained, with four 
different types, two of them being white, one yellow, and 
one black. 

''Fruit No. 2. Twenty-three vines. Fifteen types very 
unlike, twelve being white and three yellow. 

*' Fruit No. 3. Two vines. One type of fruit, which is 
almost like one of the original parents. 

"Fruit No. 4. Thirty-two vines. Six types, differing 
chiefly in size and shape. 

"Fruit No. 5. Twenty vines. Nineteen types, of which 
ten were white, eight orange, one striped, and all very unlike. 

"Fruit No. 6. Thirteen vines. Eleven types, — eight 
yellow, two black, one white. 

"Fruit No. 7. One vine. 

"These offspring were just as variable as those from 
flowers not in-bred and no more likely, apparently, to 
reproduce the parent. These tests leave me without any 
method of fixing a pronounced cross of squashes, and lead 
me to think that the legitimate process of origination of 
new kinds here, as, indeed, if not in general, is a more 
gradual process of selection, coupled, perhaps, with minor 
crossing. 



Hybridization 131 

''I will relate a definite attempt towards the fixation of 
a squash that I had obtained from crossing. The his- 
tory of it runs back to 1887, when a cross was effected 
between a summer yellow crook-neck and a white bush 
scallop squash. In 1889 there appeared a squash of 
great excellence, combining the merits of summer and 
winter squashes with very attractive form, size, and color, 
and a good habit of plant. I showed the fruit to one of 
the most expert seedsmen of the country, and he pro- 
nounced it one of the most promising types he had 
ever seen; and, as he informed me that he had fixed 
squashes by breeding in and in, I was all the more anxious 
to carry out my own convictions in the same direction. 
It is needless to say that I was very happy over what I 
regarded as a great triumph. Of course, I must have a 
large number of plants of my new variety, that I might 
select the best, both for in-breeding and for crossing similar 
types. So I selected the very finest squash, having placed 
it where I could admire it for some days, and saved every 
seed of it. These seeds were planted on the most con- 
spicuous knoll in my garden in 1890. It was soon 
evident that something was wrong. I seemed to have 
everything except my squash. One plant, however, bore 
fruits almost like the parent, and upon this I began my 
attempts towards in-breeding. But flower after flower 
failed, and I soon saw that the plant was infertile with itself. 
Careful search revealed two or three other plants very 
like this one, and I then proceeded to make crosses with 
them. I was equally confident that this method would suc- 
ceed. When I harvested my squashes in tlie fall and took 
account of stock, I found that the seeds of my one squash 



132 



Plant-Breeding 



had given just as many different types as there were 
plants, and I actually counted one hundred and ten kinds 
distinct enough to be named and recognized. Still con- 
fident, in 1891 I planted the seeds of my few crosses, and 
as the summer days grew long and the crickets chirped 
in the meadows, I watched the expanding squash blossoms 
and wondered what they would bring forth. But they 




Fig. 36. 



Hybrid citrange and its parents, Citrus (or Poncirus) trifoliata 
and common sweet orange. 



brought only disappointment. Not one seed produced a 
squash like the parent. My squash had taken an unscien- 
tific leave of absence, and I do not know its whereabouts. 
And when the frost came and killed every ambitious blos- 
som, my hope went out and has not yet returned ! " ^ 

Important hybrids of fruits and vegetables. — Let us 
now recall how many undoubted hybrids there are, named 

1 Bailey, "Plant-Breeding," earlier editions. See also, "A Medley of 
Pumpkins," Proc. Intern. PI. Breeding Conf., New York City. 



Hybridization 



133 



and known, among our fruits and vegetables. In grapes 
there are the most. There are Rogers' hybrids, as the 
Agawam, Lindley, Wilder, Salem, and Barry ; and there 
is some reason for supposing that the Delaware, Catawba, 
and other varieties are of hybrid origin. And many 
hybrids have come to notice lately through the work of 




POMELO ? 





.HYBRID TANGELO 



TAN&ELO 



rANDELO 



Fig. 37. — Hybrid tangelo and its parents, pomelo and tangerine. 



Munson and others. But it must be remembered that 
grapes are naturally exceedingly variable, and the specific 
limits are not well known, and that hybridization among 
them lacks much of that definiteness which ordinarily 
attaches to the subject. In oranges, hybrid citranges and 
tangelos made by Webber and Swingle are now reaching 
considerable commercial importance (Figs. 36-39). In 



134 



Plant- Breeding 




Fig. 38. — Samson tangelo. § natural size. (Adapted from Yearbook.) 



Hybridization 



135 




Fig. 39. — Citranges (hybrids of orange and Citrus trifoliata). Top 
fruit Citrus (or Poncirus) trifoliata. Top pair, rusk citrange. 
Bottom pair, Willits citrange. f natural size. (Reduced from 
colored figures in Vearbook of the Department of Agriculture.) 



136 Plant-Breeding 

pears there is the Kieffer class. In apples, peaches, plums, 
cherries, and currants, there are no important recognized 
commercial hybrids. In blackberries there is the black- 
berry-dewberry class, represented by the Wilson Early and 
others. Some of the raspberries, as the Philadelphia and 
Shaffer, are hybrids between the red and black species. 
Hybrids have been produced between the raspberry and 
blackberry by two or three persons, but they possess 
no /promise of economic results. It is probable that 
some of the gooseberries are hybrids. Among all the 
list of garden vegetables (plants which are propagated 
by seeds) there is apparently not a single important 
recorded hybrid ; and the same is true of wheat, — unless 
the Carman wheat-rye varieties become prominent, — 
oats, the grasses, and other farm crops (Fig. 40). But 
among ornamental plants there are many ; and it is signifi- 
cant that the most numerous, most marked, and most 
successful hybrids occur in the plants most carefully 
cultivated and protected, those, in other words, that are 
farthest removed from all untoward circumstances and an 
independent position. This is nowhere so well illustrated 
as in the case of cultivated orchids, in which hybridization 
has played no end of freaks, and in which, also, every 
individual plant is* nursed and coddled.^ With such 
plants the struggle for existence is reduced to its lowest 
terms ; for it must be borne in mind that, even in the 
garden, plants must fight severely for a chance to live, 
and even then only the very best can persist, or are even 
allowed to try. 

1 Consult E. Bohnhof, " Dictionnaire des Orchidees Hybrides," Paris, 
1905 ; also the recent Sanders lists. 



Hybridization 



137 



This list of hybrids is much more meager than most 
catalogues and trade-Ksts would have us believe. It is, 
of course, equivalent to saying that most of the so-called 
hybrid fruits and vegetables are doubtful. There is every- 




FiG. 40. — Teosinte and its hybrids with Indian corn: a and h, ears of 
teosinte, showing an entire absence of cob, kernels being attached to 
each other ; c and d, ears of first-generation cross of teosinte and 
Indian corn; e and /, Zea canina, a fourth-generation hybrid of 
teosinte and corn. All are natural size and were grown by the 
Department of Agriculture in 1900 on the Potomac Flats near 
Washington, D.C. 

where a misconception of what a hybrid is, and how it 
comes to exist ; and yet, perhaps because of this indefinite 
knowledge, there is a wide-spread feeHng that a hybrid 
is necessarily good, while the presumption is directly 
the opposite. The identity of a hybrid in the popular 



138 Plant-Breeding 

mind rests entirely on some superficial character, and 
proceeds upon the assumption that it is necessarily inter- 
mediate between the parents. Hence, we find one of our 
popular authors asserting that, because the kohl-rabi bears 
its thickened part midway of its stem, it is evidently 
a hybrid between the cabbage and turnip, which bear 
respectively the thickened parts at the opposite extrem- 
ities of the stem! And then there are those who con- 
found the word hybrid with high-bred, and who build 
attractive castles upon the unconscious error. And thus 
is confusion confounded! 

Influence of sex on hybrids. — But, before leaving this 
subject of hybridization, we must speak of the old yet 
common notion that there is some peculiar influence 
exerted by each sex in the parentage of hybrids. It 
was held by certain early observers, of whom the great 
Linnaeus was one, that the female parent determines the 
constitution of the hybrid, while the male parent gives 
the external attributes, as form, size, and color. The 
accumulated experience of nearly a century and a half 
appears to contradict this proposition, and Focke, who has 
gone over the whole ground, positively declares that it is un- 
true. There are instances, to be sure, in which this old idea 
is affirmed, but there are others in which it is contradicted. 
It is usually impossible to determine beforehand which 
parent is the stronger. It is certain that strength does not 
lie in size, neither in the high development of any character. 
It appears to be more particularly associated with what 
we call fixity or stability of character, or the tendency 
towards invariability. 

*' This has been well illustrated in my own experiments 



Hybridization 139 

with squashes, gourds, and pumpkins. The common 
httle pear-shaped gourd will impress itself more strongly 
upon crosses than any of the edible squashes and pumpkins 
with which it will effect a cross, whether it is used as male 
or female parent. It contains many dominant unit- 
characters. Even the imposing and ubiquitous great 
field pumpkin which every New Englander associates 
with pies, is overpowered by the Uttle gourd. Seeds from 
a large and sleek pumpkin which had been fertilized by 
gourd pollen produced gourds and small hard-shelled 
globular fruits which were entirely inedible. A more inter- 
esting experiment was made between the handsome 
green-striped Bergen fall squash and the little pear gourd. 
Several flowers of the gourd were pollinated by the Ber- 
gen in 1889. The fruits raised from these seeds in 1890 
were remarkably gourd-hke. Some of these crosses were 
pollinated again in 1890 by the Bergen, and the seeds were 
grown in 1891. Here, then, were crosses into which the 
gourd had gone once and the Bergen twice, and both 
parents are to all appearances equally fixed, the difference 
in strength, if any, attaching rather to the Bergen. Now, 
the crop of 1891 still carried pronounced characters of the 
gourd. Even in the fruits that most resembled the Ber- 
gen, the shells were almost flinty hard, and the flesh, even 
when thick and tender, was bitter. Some of the fruits 
looked so much like the Bergen that I was led to think 
that the gourd had largely disappeared. The very hard 
but thin paper-Hke shell which the gourd had laid over 
the thick yellow flesh of the Bergen, I thought might 
serve a useful purpose, and make the squash a better 
keeper. And I found that it was a great protection, for 



140 Plant-Breeding 

the squash could stand any amount of rough-handUng, 
and was not even injured b}^ ten degrees of frost. All 
this was an acquisition, and, as the squash was handsome 
and exceedingly productive, nothing more seemed to be 
desired. But it still remained to have a squash for dinner. 
The cook complained of the hard shell, but, once inside, 
the flesh was thick and attractive, and it cooked nicely. 
But the flavor ! Dregs of quinine, gall, and boneset ! 
The gourd was still there ! " ^ 

Uncertainties of pollination. — We have now seen that 
uncertainty follows hybridization, as well as the mere act 
of poUination. Between some species which are closely 
allied and which have large and strong flowers, four- 
fifths of the attempts towards cross-poUination may be 
successful ; but such a large proportion of successes is 
not common, and it may be infrequent even in pollination 
between plants of the same species or variety. Some of 
the failure is due in many cases to unskillful operation, but 
even the most expert operators fail as often as they suc- 
ceed in promiscuous poUinating. There is good reason to 
believe, as Darwin has shown, that the failure may be due 
to some selective power of individual plants, by which 
they refuse pollen which is, in many instances, acceptable 
to other plants even of the same variety or stock. The 
lesson to be drawn from these facts is that operations 
should be as many as possible, and that discouragement 
should not come from failure. 

"Two hundred and thirty-four pollinations of gourds, 
pumpkins, and squashes, mostly between varieties of one 
species {Cucurhita Pepo), and including some individual 

1 Bailey, earlier editions of " Plant-Breeding." 



Hybridization 141 

pollinations, gave one hundred and seventeen failures and 
one hundred and seventeen successes. These crosses 
were made in varying weather, from July 28 to August 30. 
In some periods nearly all the operations would succeed 
and at other times most of them would fail. I have 
always regarded these experiments as among my most 
successful ones, and yet but half of the polKnations 'took.' 
But one must not understand that I actually secured seeds 
from even all these one hundred and seventeen fruits, 
for some of them turned out to be seedless, and some were 
destroyed by insects before they were ripe, or they were 
lost by accidental means. A few more than half of the 
successful poUinations — if by success we mean the for- 
mation and growth of fruit — really secured us seeds, 
or about one-fourth of the whole number of efforts. 

'' Twenty pollinations were made between potato flowers, 
and they all failed ; also, seven poUinations of red peppers, 
four of husk tomato, two of Nicotiana affinis upon petunia 
and two of the reciprocal cross, twelve of radish, one of 
Mirahilis jalapa upon M. longiflora and two of the recip- 
rocal cross, three Convolvulus major upon C. minor and 
one of the reciprocal, one muskmelon by squash, two 
muskmelons by watermelon, and one muskmelon by cu- 
cumber. 

''This is but one record. Let me give another : — 
"Cucumber, ninety-five efforts: fifty-two successes; 
forty-three failures. Tomato, forty-three efforts : nine- 
teen successes ; twenty-four failures. Egg-plant, seven 
efforts : one success ; six failures. Pepper, fifteen efforts : 
one success ; fourteen failures. Husk-tomato, forty-five 
efforts : forty-five failures. Pepino, twelve efforts : twelve 



142 Plant-Breeding 

failures. Petunia by Nicotiana affinis, eleven efforts : 
eleven failures. Nicotiana affinis by petunia, six efforts : 
six failures. General Grant tobacco by Nicotiana affinis, 
eleven efforts : eight successes ; three failures. Nicotiana 
affinis by General Grant tobacco, fifteen efforts : fifteen 
failures. General Grant tobacco by General Grant 
tobacco, one effort : one success. Nicotiana affinis by 
Nicotiana affinis, three efforts : two successes ; one failure. 
Tuberous begonia, five efforts : five successes. 

"Total, three hundred and twelve efforts: eighty-nine 
successes, two hundred and twenty-three failures." ^ 

Graft-hybrids. — It is well known that, when two varie- 
ties or aUied species are grafted together, each retains its 
distinctive characters. But to this general, if not uni- 
versal, rule there are on record several alleged exceptions, 
in which either the cion is said to have partaken of the 
qualities of the stock, the stock of the cion, or each to 
have affected the other. Supposing any of these in- 
fluences to have been exerted, the resulting product would 
deserve to be called a graft-hybrid. 

It is clearly a matter of great interest to ascertain 
whether such formation of hybrids by grafting is really 
possible ; for, even if one example of such formation could 
be unequivocably proved, it would show that sexual 
and asexual reproduction are essentially identical. 

The case of Cytisus Adami (Figs. 41, 42). — The cases of 
alleged graft-hybridization are exceedingly few, considering 
the enormous number of grafts that are made every year 
by horticulturists and have been made for centuries. 

Of these cases, one of the most celebrated is that of 

^ Bailey, earlier editions. 



Hybridization 



143 




Fig. 41. — Cytisus Adami, A, A', A"; B, a branch of C. lahurum, L, 
U, L", with numerous racemes bearing ripe pods. 

Adam's laburnum {Cytisus Adami). This plant is now 
flourishing in many places throughout Europe, all of the 
trees having been raised as cuttings from the original 
graft, which was made by inserting a bud of the purple 



144 



Plant-Breeding 




Fig. ^2. — Cytisus Adami, A, A', bearing at 7 a bunch of twigs of 
C. purjmreus, P, H, and /. 



Hybridization 145 

laburnum {Cytisus purpureus) into a stock of the yellow 
{Cytisus laburnum). M. Adami, who made the graft at 
Vitry, near Paris, about 1826, has left on record that from 
it there sprang the existing hybrid. There can be no 
question as to the truly hybrid nature of the latter. It 
is, however, absolutely sterile, and is multiphed by grafts. 
It bears three kinds of flowers — some pink, others large 
and yellow, others small and purple. That is to say, it 
bore its own hybrid flowers, also those of its two parents, 
and the leaves and ramifications of the parts of the tree 
which bore these three kinds of flowers were hkewise of 
the same three kinds and could be distinguished even in 
winter. 

Strasburger made a careful cytological study of Cytisus 
Adami, which has been retained in cultivation ever since 
its origin some eighty years ago. He came to the con- 
clusion that Cytisus Adami was a real sexual hybrid and 
not a graft-hybrid. He thinks that if the latter were 
true, the nuclei of the hybrid would show a double number 
of chromosomes. This, of course, implies that in hybrids 
arising otherwise than sexually, assuming that a nuclear 
fusion would precede the formation of such a hybrid, 
there would be no reduction division of the nuclei com- 
parable to that which normally occurs before the fusion 
of the sexual cells in normal fertiUzation. 

Nemec, however, thinks that a reduction division 
does occur and there is, therefore, no reason to expect 
an increase in the number of chromosomes in the cells 
of the hybrid. If such a reduction does occur, Cytisus 
Adami would show the same number of chromosomes as 
C. laburnum, which has the same number as C. purpureus. 

L 



146 Plant-Breeding 

Winkler's Solanum graft-hybrids. — Professor H. Winkler 
of Tubingen has carefully performed experiments in 
making graft-hybrids with the black nightshade, Solanum 
nigrum, and two varieties of the tomato, Solanum lyco- 
persicum. These two species are very distinct, and indeed 
many botanists regard the tomato as belonging to a dis- 
tinct genus lycopersicum, so that Winkler's graft-hybrids 
may be regarded as bigeneric hybrids. SeedUngs of each 
were grown and reciprocal grafts made. The graft and 
stock united readily whether the nightshade or the tomato 
was used as the stock. 

Naturally the majority of the shoots arising from the 
cut surface of the stem were either pure nightshade or 
pure tomato. But finally shoots were observed which 
were evidently of mixed origin. The first of these graft- 
hybrids were obviously composed of pure elements 
derived from the two parents. Some of these shoots were 
almost equally divided by a median Hne, on one side of 
which the organs — stem, leaf — were those of the night- 
shade, while on the other the organs were evidently derived 
from the tomato. It is obvious that such unusual forms, 
which Winkler called '^Chimsera,'' are not hybrids in any 
true sense of the word, but have arisen from buds which 
contain the tissue of the two parent formed at the junction 
of the stock and graft. 

Later on there developed, however, shoots which were 
evidently of hybrid origin. Cell fusion had unquestion- 
ably taken place. Several hybrids with different attributes 
were produced. These have been given different names 
by Professor Winkler, and may be described as follows : — 

1. Solanum tubingense is intermediate in the size and 



Hybridization 147 

shape of the leaves and the color and type of the flowers 
between the nightshade and the tomato. The fruit is 
very much Uke that of the nightshade, but is rather larger, 
and although it is black there are some traces of the red 
or yellow color of the tomato. 

2. Solarium proteus has very variable leaves, which, 
on the whole, are more divided than those of S. tuhingense, 
while in the characters of the flowers and the fruit it is 
more like the tomato than like the nightshade. 

3. Solanum Kolreuterianum, and 

4. Solanum Gdrtnerianum. These forms have been 
produced several times. The first is more like the tomato, 
the second more like the nightshade, but each differs in 
important particulars from either of the parents. 

5. Solanum Darwinianum. The point of especial inter- 
est in connection with this form is that of all the so-called 
^^graft-hybrids" secured by Winkler this seems to be the 
only one which is hkely to prove a hybrid in the strict 
sense of the word. The fruit of this plant, unhke the 
others, was sterile, no perfect seeds being formed. The 
fruit itself is a round small berry Uke the fruit of the night- 
shade in form, but having the color and structure of the 
tomato. 

Are these real graft-hybrids f — In all of these forms when 
seed was produced at all, it produced seedlings of one parent 
or the other, never producing the apparent hybrid. 

It has been suggested by Bauer that these apparent 
true hybrids might be chimseras of a type which he has 
called ''periclinal," i.e. the outer tissues are derived 
from one parent, and the inner tissues from the other, 
but none of the tissues themselves are of hybrid origin. 



148 Plant-Breeding 

This explanation has also been applied to Cytisus hybrids 
in which it has been shown that the epidermal tissues were 
strikingly Uke those of C. purpureus, while the inner tissues 
were like those of C. laburnum. 

In a later paper, Winkler arrives at the following 
conclusions : — 

Hybrids may be arranged in two groups, sexual and 
graft-hybrids. The latter may be divided into three 
classes according to the theoretical possibiUty of their 
method of origin, viz. : (1) Fusion graft-hybrids arising 
from a fusion of two somatic cells derived from distinct 
species. (2) ''Influenced" graft-hybrids which arise from 
specific influences of one graft component upon the other 
without cell fusion (as through chemical substances, trans- 
location of cytoplasm, etc.). (3) Chimaeras, in which 
specifically pure cells from both graft components are 
combined to form a new individual. These chimseras may 
be : (a) Sectorial chimseras in which the two sorts of cells 
in the growing point are divided by a longitudinal plane. 
(b) PericUnal chimseras in which the perichnal cell layers 
of the growing point are furnished respectively from one or 
the other parent form, (c) Hyper-chimseras in which the 
growing point is made up of a mosaic of cells derived from 
the two parent forms. 



CHAPTER VII 
HEREDITY 

All plants arise from parents more or less like them- 
selves. This reproduction has a visible material basis in 
the egg-cells and pollen-grains liberated from the parental 
bodies. By inheritance is meant all the qualities which 
have their physical basis in the fertilized egg-cell, the ex- 
pression of which results in the organism. ''Thus/' says 
Thomson, ''heredity is no force, no principle, but a con- 
venient term for the genetic relation between successive 
organisms." 

The inheritance of plants may be studied by considering 
parents and their offspring collectively or by studying 
the separate characters and their modes of transmission. 
The former is statistical, the latter, analytical. Studies 
of heredity from both points of view are being extensively 
conducted by the biometricians on the one hand and the 
mendehans on the other. 

Heredity studied collectively. — "To define heredity," 
says Davenport, "as the direct and personal relation 
between the individual parent and the individual offspring 
is not only to restrict its meaning within too narrow Umits, 
but to destroy its significance to the breeder and deceive 
him as to the actual facts of transmission during descent. 
* Heredity' properly refers to the group that constitutes 

149 



150 



Plant-Breeding 



Number of Tubers — 3909 



V 


1.5 


3.5 


5.5 


7.5 


9.5 


11.5 


13.5 


15.5 


17.5 


19.5 


21.5 


23.5 


1.5 




1 


2 








1 












3.5 


1 


6 


6 


3 


2 


2 














5.5 




4 


6 


8 


8 


5 


G 


1 


2 








7.5 




4 


7 


11 


8 


8 


3 


2 










9.5 




2 


7 


17 


13 


15 


4 


1 


3 


1 




1 


11.5 




2 


2 


14 


11 


14 


6 


3 


4 


2 






13.5 






1 


5 


4 


10 


7 


3 


5 




1 


1 


15.5 


1 


1 


1 


1 


5 


9 


6 


5 


2 


3 


3 


1 


17.5 








2 


4 


2 


3 


2 


2 


3 




1 


19.5 






1 




1 


2 


2 






2 


2 




21.5 










2 


1 




1 


1 


1 




2 . 


23.5 










2 


1 




1 


1 


1 






25.5 












1 






1 








27.5 


























29.5 








1 












( 






31.5 


























33.5 


















1 








4 


2 


20 


33 


62 


60 


70 


38 


il9 


22 


13 


6 


6 


^ 


3 


^ 


Lt 


^ 


^ 


^ 


^ 


( LC 


c 


LO 


o 


o 


1 "v 


re 


t^ 


1—1 






it 

X 


Lt 


C: 


X 
CO 


CO 
lO 
01 


o 
M 


1—1 


O 


i> 


i> 


t^ 


r^ 


t^ 


?c 


^ 


o 


^ 


CO 


CO 


o 

CO 


Q 


C5 
1 


1 


1 




1 


+ 


•M 


rt^ 


^"^ 


X 


^ 


01 




S 


?i 


CI 


s 


X 


-. 


?l 


i; 


c: 


X 


2- 


01 


Q 


C5 


Lt 




rc 


(M 




Lt 


X 


CO 


X 


- 


lO 


© 


00 

1—1 


,i 


1—1 


X 


^ 


^ 


23 


1—1 

ro 


X 
1— ( 


lO 


LO 




c 


1—1 


00 

1— i 


C5 

C 

1—1 


00 


1— 1 




?5 


i-H 

!^5 


CO 
X 


lO 
X 


3 


o 



Heredity 



151 



25.5 


27.5 


41.5 


43.5 


/lO 


/ool^og 


Do9 -D^o9 


-D^09/o9 


2P 






. . . . i 


1 


4 


6 


-9.83 96.62 


386.48 


165.14 












20 


70 


-7.83 61.30 


1226.00 


814.32 












40 


220 


-5.83 33.98 


1359.20 


443.08 




1 








44 


330 


-3.83 14.66 


645.04 


347.76 










1 


65 


617.5 


-1.83 3.34 


217.10 


92.41 












58 


667 


0.17; .02 


1.16 


- 4.18 












37 


499.5 


2.17 4.70 


173.90 


119.56 


2 


1 








41 


635.5 


4.17 17.38 


712.58 


535.01 












19 


332.5 


6.17 38.06 


723.14 


318.98 












10 


195 


8.17 66.74 


667.40 


285.95 












8 


172 


10.17 103.42 


827.36 


410.86 




1 








7 


164.5 


12.17 148.10 


1036.70 


390.65 












2 


51.0 


14.17 200.78 


401.56 


93.52 

















16.17 261.46 
















1 


29.5 


18.17 330.14 


330.14 


-67.22 

















20.17 406.82 






1 








1 2 


67 


22.17 491.50 


983.0 


456.70 


3 


3 




1 358 


4057 




9690.76 4402.54 

1 


u^ 


L': XT. c 




1 






3/o9 = 11.33 ± .182 










J/io = 11.20 ± .182 


i 


o 

1—1 




1 


O"09 

r 


= 5.20 ± .130 
= 5.23 ± .131 

4402.54 ... 


2 




c: 


r: Oi 


358(5.2) (5.23) 


?5 




X 


^^. .6745(1 -r^) 

.6745 (.80) _^ 03 
18.9 








CO 
1—1 


1> C: 









152 Plant-Breeding 

the parentage and the related group that constitutes 
the offspring." 

The coefficient of heredity. — The degree of inheritance 
between a parental group of plants and their corresponding 
group of offspring is determined by the use of a correlation 
table. The degree of correlation or the resemblance is 
determined between the parents and offspring. This may 
be expressed mathematically and the result is known as 
the ''coefficient of heredity." The latter is, therefore, 
nothing more nor less than the correlation coefficient (r) 
obtained from a table in which two sets of individuals 
related by descent are tabulated with respect to the same 
character. The coefficient of heredity is expressed as a 
decimal, somewhere between and 1. The nearer 1, 
the greater the closeness of resemblance between parents 
and offspring, and conversely the nearer 0, the smaller 
the degree of resemblance. 

In the table (pp. 150-151) will be found the number of 
tubers in hills of potatoes in 1909 as compared with the off- 
spring from these hills in 1910. For example, there were 3 
hills of seedUng potatoes having either 7 or 8 tubers in 1909 
represented in the table by the midpoint 7.5 which gave 
offspring in 1910 having either 3 or 4 tubers (3.5) ; 8 
parental hills numbering either 7 or 8 tubers in 1909 which 
produced offspring in 1910 having either 5 or 6 tubers ; 
11 parental hills having the same number of tubers as 
above which produced offspring having either 7 or 8 hills, 
and so forth for each number in the table : — 

Notation. — 

n = Total number of individuals in the population, 
equals summation of all frequencies. 



Heredity 153 

/o9 = Class frequencies of total population in 1909. 

Fo9 = Value or measurement corresponding to a given 
frequency in 1909. 

Mo9 = Mean number of potatoes per hill in 1909. 

Do9 = Deviation of number of tubers per hill from mean, 
1909. 

O-09 = Standard deviations of number of tubers per hill, 
1909. 

/lo = Class frequencies of total population in 1910. 

7^0 = Value or measurement corresponding to a given 
frequency in 1910. 

Mio = Mean number of potatoes per hill in 1910. 

Dio = Deviation of numbers of tubers per hill from 
mean, 1910. 

o-io = Standard deviation of number of tubers per hill, 
1910. 

r = Coefficient of correlation. 

The process of finding the mean and standard devia- 
tion is the same as is given in Chapter IV, so that the 
only column that needs explanation is the one headed 

As an example, we will take the column on the 1910 
tubers, beginning with 15.5. The figures 1, 1, 1, 1, 5, 
9, 6, 5, 2, 3, 3, 1, 2, 1 are known as a horizontal array ; 
similarly the vertical columns are known as a vertical 
array. We will now show how 535.01 in 5P column is 
obtained. 

The first number after 15.5 is 1. Going down the verti- 
cal column to column Dio, we find - 9.7, which is multi- 
pUed by 1 ; the same process is gone through for each 
number following 15.5 and the algebraic sum is taken, 



154 Plant-Breeding 

which is multiplied by 4.17, found in column D09 opposite 
15.5. So the result is as follows : — 

4.17+ l(-9.7) +l(-7.7)+ 1 (-5.7)+ l(-3.7) + 5(-1.7) + 
9(0.30) +6(2.3) +5(4.3) +2(6.3)+3(8.3) +3(10.3) + 1(12.3) 
+ 2(14.3)+ 1(16.3) = 535.01. 

Having obtained all the numbers in the 2P column, the 
sum is taken and the coefficient of correlation is found ac- 
cording to the following formula : — 

r= 4402.54 ^^^^^ 



358(5.20) (5.23) 



Conception of unit-characters. — Most recent studies are 
analytical in their nature. We now conceive of plants 
and animals to be composed of separately heritable units 
known as unit-characters. It is not possible at present to 
say exactly what a unit-character is, but we may call it 
the smallest heritable part or attribute a plant may 
possess. For example, the color of the flower, size and 
shape of leaf, height of the plant, susceptibiUty or im- 
munity to disease, and so forth, may be unit-characters. 

Knowledge of heredity has come through experimental 
breeding. — Much has been written and many conjectures 
made by earher horticulturists in their attempt to classify 
hybrids so that inheritance could be found to proceed in 
an orderly and regular manner. All of these attempts 
had been more or less failures until Gregor Mendel, an 
Austrian monk, began a series of classic experiments in 



Heredity 155 

crossing garden peas. Mendel's work, however, was little 
known at the time and did not receive public recognition 
until many years afterwards. 

Rediscovery of MendeVs work by de Vries and others. — 
de Vries made a thorough search of the literature of plant 
evolution. In an American publication ^ he saw a ref- 
erence to an article on plant hybrids by G. Mendel, 
pubHshed in 1865 in the proceedings of a natural history 
of Briinn in Austria. 

On looking up this paper he was astonished to find that 
it discussed fundamental questions of hybridization and 
heredity, and that it had remained practically unknown 
for a generation. In 1900 he pubUshed an account of it, 
and this was soon followed by independent discussions 
by Correns, Tschermak, and Bateson. In May, 1900, 
Bateson gave an abstract of Mendel's work before the 
Royal Horticultural Society of England; and later the 
society published a translation of Mendel's original paper. 
It is only within the last 10 or 12 years that a knowledge 
of Mendel's work has become widespread in this country. 
Perhaps the agencies that are most responsible for dis- 

1 The following extract from a letter from Professor de Vries (printed 
here by permission) will explain the reference in the text : " Many years 
ago you had the kindness to send me your article on ' Cross-breeding and 
Hybridizing ' of 1892 ; and I hope it will interest you to know that it was 
by means of your bibliography therein that I learnt some years after- 
wards of the existence of Mendel's papers, which now are coming to so 
high credit. Without your aid I fear I should not have found them at 
all." My reference to Mendel in the bibliography referred to was taken 
from Focke's writing. I had not seen Mendel's paper. The essay, 
"Cross-breeding and Hybridizing," formed Chapter II of the old 
"Plant-Breeding"; but the bibliography that accompanied it was not 
reprinted until the second edition of the book. — L. H. B. 



156 Plant-Breeding 

semination of the mendelian ideas in America are the in- 
struction given by Webber and others in the Graduate 
School of Agriculture at Columbus, Ohio, in the summer 
of 1904 and the prolonged discussion before the Interna- 
tional Conference on Plant Breeding at New York in the 
fall of 1902. Since that time many articles on the subject 
have appeared from our scientific press. 

Mendel's work is important because it cuts across many 
of the current notions respecting hybridization. As 
de Vries' discussions call a halt in the current beUef re- 
garding the gradualness and slowness of evolution, so 
Mendel's call a halt in respect to the common opinion 
that the results of hybridizing are largely chance, and that 
hybridization is necessarily only an empirical subject. 
Mendel found uniformity and constancy of action in 
hybridization, and to explain this uniformity he proposed 
a theory of heredity. 

One of the most significant points connected with 
Mendel's work is the great care he took to select plants 
for his experiments. He thought that hybridism is a 
complex and intricate subject, and that, if we are ever to 
discover laws, we must begin with the simplest and least 
compHcated problems. He was aware of the general 
opinion that the most diverse and contradictory results are 
Ukely to follow any hybridization. He conceived that 
some of this diversity may be due to instability of parents 
rather than to the proper results of hybridizing. He also 
saw that he must exclude all inter-crossing in the progeny. 
Furthermore, the progeny must be numerous, for, since 
incidental and aberrant variation may arise in the plants, 
it is only by a study of averages of large numbers that the 



Heredity 157 

true results of the hybridization are to be discovered. 
Moreover, the study must be more exact than a mere con- 
trasting and comparing of plants : character must be com- 
pared with character. 

MendeVs experiments. — The garden pea seemed to fulfill 
all of the requirements. Mendel chose well-marked hor- 
ticultural races or varieties. He grew these two years 
before the experiment proper was begun in order to de- 
termine their stability or trueness to type. When the 
experiments were finally begun, he used only normal 
plants as parents, throwing out such as were weak or 
aberrant. Peas are self-fertile. It was to be expected 
that under such conditions the hybrid offspring would 
show uniformity of action ; and it did. 

In order to study the behavior of the hybrids, it was 
necessary to choose certain prominent marks or characters 
for comparison. Seven of these characters were chosen 
for observation. These marks pertain to seed, fruit, 
position of flowers, and length of stem, and they may be 
assumed to be representative of all other characters in 
the plant. These characters were paired (practically 
opposites) as long-stem vs. short-stem, round-seed vs. 
angular-seed, inflated pods vs. constricted pods. They 
were '^ constant" and '^differentiating." Of course every 
parent plant possessed one or the other of every pair of 
contrasting characters ; but in order to facihtate his 
studies, Mendel chose a special set of parents to illustrate 
each character. 

The seed-shape characters were roundness and angu- 
larity — the former being the ''smooth" pea of gardeners 
and the latter the "wrinkled" pea. Let us suppose that 



158 Plant-Breeding 

twenty-five flowers on round-seeded plants were cross- 
pollinated in the summer of 1900 with pollen from angular - 
seeded plants, or vice versa, and that an average of four 
seeds formed in each pod. With the death of the parent 
plants the old generation ended, and the 100 seeds that 
matured in 1900 — the year in which the cross was made — 
began the next generation ; and these 100 seeds were 
hybrids. Now, all of these 100 seeds were round. Round- 
ness in this case was '^dominant." (Dominance per- 
taining to the vegetative stage of the plant of course would 
not appear until 1901, when the seeds ^^grow.") These 
seeds are sown in the spring of 1901. If each seed be 
supposed to give rise to four seeds, — or 400 in all, — this 
next generation of seeds (produced in 1901) will show 
300 round and 100 angular seeds. That is, the other seed- 
shape now appears in one-fourth of all the progeny; this 
character is said to have been ''recessive" in the first 
hybrid generation. If the 100 angular seeds, or reces- 
sives, are sown in 1902, it will be found that all the progeny 
will be angular-seeded or will "come true"; and this 
occurs in all succeeding generations, providing no crossing 
takes place. If the 300 round seeds, or dominants, are 
sown in the spring of 1902, it will be found that 100 of them 
produce dominants only, and that 200 of them behave as 
before — one-fourth giving rise to recessives and three- 
fourths to dominants ; and this occurs in all succeeding 
generations, providing no crossing takes place. In other 
words, the three-fourths of dominants in any generation 
are of two kinds, — one-third that produce only dominants, 
and two-thirds that are hybrids. That is, there is con- 
stantly appearing from the hybrids one-fourth that are 



Heredity 



159 



recessives, one-fourth that are constant dominants, and 
one-half that are dominants to all appearances, but which 
in the next generation break up again into dominants 
and recessives. This one-half part that breaks up into 
the two characters are the true hybrids ; but they are 
hybrids only in the sense that they hold each of the two 
parental characteristics — roundness and angularity — in 
their purity and not as blends or intermediates ; and these 
two characteristics reappear in all succeeding generations 
in a definite mathematical ratio. Proportionally, these 
facts may be expressed as follows : — 



1900. 



1901. 



1 seed 




16 R 



It will be seen that two-thirds of the dominants break 
up the following year into one-fourth constant dominants, 
one-fourth recessives, and one-half that again break up, 
the half that break up being the hybrids. This formula 
for the hybrids is Mendel's law. In words, it may be 
expressed as follows : Differentiating characters in plants 
reappear in their purity and in mathematical regularity 



160 Plant-Breeding 

in the second and succeeding hybrid offspring of these 
plants; the mathematical law is that each character 
separates in each of these generations in one-fourth of the 
progeny and thereafter remains true. In concise figures, 
it is expressed as follows : — 

ID: 2DR:1R. 

1 D and 1 R come true, but 2 DR breaks up again into 
dominant and recessives in the ratio of 3 to 1. 

Mendel found that this law holds more or less for the 
other characters that he studied in the pea, as well as for 
the seed-shape. He did not conclude, however, that it 
holds good for all plants, but left the subject for further 
investigation. It will be seen at once that it will be a 
very difficult matter to follow this law when many char- 
acters are to be constrasted, particularly when the char- 
acters are quantitative, or qualitative which grade into 
each other. 

The dominant characters pertain to either parent. Some 
of them may come from the seed parent and some from 
the pollen parent. When this roundness is dominant from 
the male parent, there can be seen the immediate effect of 
pollen, the same as if the dominant roundness came from 
the female parent. In the case of the pea, the seed-content 
is embryo and we are not surprised to find this immediate 
effect of pollen. In those plants in which the embryo 
is embedded in endosperm, however, the effect of the cross- 
fertilization is not seen until the seed has been planted 
and produced a new generation. The endosperm is a part 
of the female parent and is not ordinarily changed by the 
process of cross-fertilization. In the case of a few plants, 



Heredity 161 

of which the Indian corn is the most conspicuous example 
(Fig. 43), there is double fecundation, both the embryo and 
endosperm being fertilized, and hence if the male parent 
contains dominant characters, they will be seen immediately 
because of the cross-fertilized endosperm. This is called 
Xenia and has been carefully worked out by de Vries, 
Webber,^ and others. 

MendeVs numerical residts.^ — 

In the experiments conducted by Mendel with peas the 
relative numbers obtained for each pair of differentiating 
characters are as follows : — 

Experiment 1. — Form of seed. From 253 hybrids, 
7324 seeds were obtained in the second trial year. Among 
them were 5474 round and roundish and 1850 angular, 
wrinkled ones. Therefore, the ratio 2.96 is to 1 is de- 
duced. 

Experiment 2. — Color of albumen. 258 plants yielded 
8023 seeds, 6022 yellow and 2001 green ; their ratio, there- 
fore, is 3.01 to 1. 

Experiment 3. — Color of seed-coats. Among 929 
plants, 705 bore violet-red flowers and gray-bro^\Ti seed- 
coats ; 224 had white flowers and white seed-coats, giving 
the proportion of 3.15 to 1. 

Experiment 4. — Form of pods. Of 1181 plants, 882 
had them simply inflated and in 299 they were constricted. 
Resulting ratio 2.95 to 1. 

Experiment 5. — Color of unripe pods. The number 

1 Bull. 22, Div. of Veg. Phys. and Path., U. S. Dept. of Agric, 1900. 

2 The following is taken from a translation of Mendel's article as given 
by Bateson, and slightly revised. See Bateson-Mendel's "Principles of 
Heredity," Appendix. 

M 




Fig 43.-Mendelisminmaize.-StowellEvergreen (^-^^/J1^>J^^^^^ 
inated with Indian flour corn, giving a hybrid similar to the latter the 
first veaT This was self-pollinated, giving the ear o^^th^J^^^^*' ^^^ 
pollinated with the evergreen, giving the ear on the left (Webber). 

162 



Heredity 163 

of trial plants was 500, of which 428 had green pods and 
152 yellow pods. Consequently these stand in the ratio 
2.82 to 1. 

Experiment 6. — Position of flowers. Among 858 cases, 
651 had inflorescence axial and 207 terminal. Ratio 3.14 
to 1. 

Experiment 7. — Length of stem. Out of 1064 plants 
in 787 cases the stem was long and in 277 short. Hence 
a mutual ratio of 2.84 to 1. 

If the results of the whole experiment be brought to- 
gether, there is found, as between the numbers of forms 
with the dominant and recessive characters, an average 
ratio of 2.98 to 1 or 3 to 1. 

The following is an account of Mendel's results with 
peas in their third hybrid generation {F^) : — 

These forms which in the F2 generation exhibit the 
recessive character do not further vary in the F^ generation 
as regards this character : they remain constant in their 
offspring. 

It is otherwise with those that possess the dominant 
character in the second generation. Of these, two-thirds 
yield offspring that display the dominant and recessive 
characters in the proportion of 3 to 1, and thereby show 
exactly the same ratio as the hybrid forms, while only 
one-third remain with the dominant character constant. 

The separate experiments yield the following results : — 

Experiment 1. — Among 665 plants which were raised 
from round seeds of the second generation, 193 yielded 
round seeds only, and remained, therefore, constant in 
this character; 372, however, gave both round and 
wrinkled seeds, in the proportion of 3 to 1. The number 



164 Plant-Breeding 

of the hybrids, therefore, as compared with the constants, 
is 1.93 to 1. 

Experiment 2. — Of 509 plants which were raised from 
seeds whose albumen was of yellow color in the second 
generation, 166 jdelded exclusively yellow,while 353 yielded 
yellow and green seeds, in the proportion of 3 to 1. There 
resulted, therefore, a division into hybrid and constant 
forms in the proportion of 2.13 to 1. 

For each separate trial in the following experiments, 
100 plants were selected which displayed the dominant 
character in the second generation, and in order to as- 
certain the significance of this, ten seeds of each were 
cultivated. 

Experiment 3. — The offspring of 36 plants yielded 
exclusively gray-brown seed-coats, while of the off- 
spring of 64 plants some had gray-brown and some 
had white. 

Experiment 4. — The offspring of 29 plants had only 
inflated pods; of the offspring of 71, on the other hand, 
some had inflated and some had constricted. 

Experiment 5. — The offspring of 40 plants had only 
green pods ; of the offspring of 60 plants, some had green 
and some yellow ones. 

Experiment 6. — The offspring of 33 plants had only 
axial flowers ; of the offspring of 67, on the other hand, 
some had axial and some terminal flowers. 

Experiment 7. — The offspring of 28 plants inherited 
the long axis, and those of the 72 plants some of the long 
and some of the short axis. 

In each of these experiments a certain number of plants 
came constant with the dominant character. For the 



Heredity 165 

determination of the proportion in which the separation 
of the forms with the constantly persistent character 
results, the first two experiments are of especial importance 
since in these a greater number of plants can be compared. 
The ratios 1.93 to 1 and 2.3 to 1 gave together almost 
exactly the average ratio of 2 to 1. The sixth experiment 
gave a quite concordant result; in the others the ratio 
varies more or less, as was only to be expected in view of 
the small number of 100 trial plants. Experiment 5, 
which shows the greatest departure, was repeated, and 
then in place of the ratio of 60 and 40 that of 65 and 35 
resulted. The average ratio of 2 to 1 appears, therefore, 
as fixed with certainty. It is, therefore, demonstrated 
that, of those forms which possess the dominant character 
in the second generation, two-thirds have the hybrid- 
characters, while one-third remain constant with the 
dominant characters. 

The ratio of 3 to 1, in accordance with which the dis- 
tribution of the dominant and recessive characters re- 
sults in the second generation, resolves itself, therefore, in 
all experiments into the ratio of 2 : 1 : 1 if the dominant 
character be differentiated according to its significance 
as a hybrid-character or as a parental one. Since the 
second generation (F2) springs directly from the seed of 
the first generation (Fi), it is now clear that the hybrids 
from seeds have one or the other of the two differen- 
tiating characters, and of those one-half develop again 
the hybrid form, while the other yields plants which re- 
main constant and receive the dominant or the recessive 
characters, respectively, in equal numbers. 

Dominance and recessiveness. — Which characters will 



166 Plant-Breeding 

be dominant in any species we cannot determine until we 
perform the experiment ; that is, there is no mark or 
attribute which distinguishes to us a priori a dominant or 
a recessive character. However, the mere fact as to 
whether the one or the other character is dominant is 
relatively unimportant, for constant dominance is no 
more a regular behavior than recessiveness is. In various 
subsequent experiments it has been found that even 
when marked dominance is not shown in the first product, 
the hybridization may follow the law in essential numeri- 
cal results. The really important points are : (1) That 
the characters typically remain pure or do not blend, 
and (2) that their reappearance follows a numerical 
order. 

Explanation of mendelian results. — After finding such 
surprising results as these, Mendel naturally endeavored 
to discover the reasons why. The product of his specu- 
lations is the theory of gametic purity (to use our present- 
day terminology), which is a partial theory of heredity. 
Every plant is the product of the egg, or female, cell 
fertilized by the sperm, or male, cell. When constant 
progeny is produced, it must be because the two cells, or 
gametes, are of like character. When inconstant progeny 
is produced, it must be because the sperm-cell is of one 
character and the egg-cell of another. When these un- 
like gametes come together, they will unite according to 
the law of mathematical probabilities, one-fourth of those 
of each kind coming together and one-half of those of 
both kinds coming together. If A and B represent the 
contrasting parental characteristics, they would combine 
as : — 



Heredity 167 

A -\-A = A'. 
A +B = AB. 
B -i-A = BA. 
B +B = BK 

A 2 and B^ are equivalent only to A and B. Since both 
of the opposed or contrasted characters cannot be visible 
at the same time, we have the following : — 

A 

B 

in which small h represents the character that for the 
time being is not able to express itself, or is recessive, and 
large B represents the same character fully expressed. 

In these gametes, the unit-characters of the plants that 
bear them are pure. Even in hybrid plants the pollen- 
grains and the egg-cells are not hybrids. According to 
the hypothesis of gametic purity, therefore, hybrids 
follow natural and numerical laws; but these laws are 
always obscured by new crossing. True intermediate 
characters do not occur. If new characters appear, it is 
because they have been recessive or latent for a genera- 
tion, or because the plant has varied from other causes ; 
they are not the proper results of hybridization, unless 
they are due to a reconstruction of characters. We may 
suppose that a new character that appears because of 
some internal change may be impressed on the gametes 
and thereby be perpetuated. The results of hybridiza- 
tion, according to the mendelian view, are not funda- 



168 Plant-Breeding 

mentally a mere game of chance, but follow a law of 
regularity of averages ; but the results are so often masked 
that it is sometimes impossible to recognize the law. 

It is a question, of course, whether the proportional 
results secured by Mendel and others express a biological 
principle, or whether they are only the numerical propor- 
tions that may be adduced from the averages of large 
numbers of combinations — whether these combinations 
are of gametes or letters, or words, or figures. It is a 
fundamental necessity that certain proportions follow 
from '^ chance " combinations often repeated. But whether 
the ''theorem of probabilities" can express a real bio- 
logical fact may well be doubted. Perhaps the basis of 
heredity is something more than the mechanico-physical 
conceptions that we habitually apply to it. 

Mendel's law of heredity is stated as follows by Bateson 
and Saunders : "The essential part of the discovery is the 
evidence that the germ-cells or gametes produced by 
cross-bred organisms may in respect of given characters 
be of the pure parental types and consequently incapable 
of transmitting the opposite character; that when such 
pure similar gametes of opposite sexes are united together 
in fertilization, the individuals so formed and their pos- 
terity are free from all taint of the cross, that there may 
be, in short, perfect or almost perfect discontinuity 
between these germs in respect of one of each pair of op- 
posite characters." 

The genetic constitutions of plants, if they are known, 
may be conveniently represented by formulae containing 
the gametic make-up of the parents entering into their 
union. At least such unit-characters as are known may 



Heredity 



1G9 



be represented in this manner. For example, RR may 
represent a plant which has been formed by the union 
of a red pollen-grain (pollen-grain from a pure red parent) 
R and a red egg-cell R. This plant if self-fertilized will 
always remain red. Similarly rr represents a plant 
which has the absence (or the opposite) of red, say, yellow. 
If a red plant R were crossed with a yellow plant r, the 
result would be a hybrid Rr. Red being dominant, the 
first generation hybrid, F\, would appear as red. 

The following method of squares will be found very 
convenient to illustrate the action of chance which governs 
the union of gametes to form the Fi hybrid plants : — 



•/? 






Pollen-grains 

I I 

R. r 



(1) 

RR 


(2) 
Rr 


(3) 
Rr 


(4) 
rr 



Square (1) represents a plant {RR) formed from the 
union of a red pollen-grain R with a red egg-cell R, 
and is pure red. Square (2) represents a hybrid plant 
{Rr) formed by r pollen-grain and R egg-cell. Square (3) 



170 



Plant-Breeding 



^ 
% 
^ 






u: 




Heredity 171 

is, the same as (2) except formed by pollen-grain R and 
egg-cell r, and square (4) is a pure recessive rr in which 
pollen-grain r united with egg-cell r. 

This may be illustrated diagrammatically in another 
manner, as in the colored plate (Fig. 44) . 

Explanation of diagram. — It is assumed that a variety 
having red flowers {R) is crossed with another variety 
having yellow flowers (r). The arrow indicates the 
direction of the cross and also the transfer of pollen from 
the anthers of the yellow variety to the stigma of the red. 
The plants produced from these fertilized ovules will 
have red flowers because redness is dominant. This Fi 
hybrid, however, contains both red and yellow qualities 
and at the time of the formation of its gametes will give 
rise to red and yellow pollen-grains and egg-cells. During 
the process of self-fertilization the law of chance will 
govern the union of the red and yellow egg-cells. These 
Fi ovules will give rise to the plants indicated by F2. 
The subsequent operations are assumed to follow regular 
mendelian ratios. 

MendeVs results with the offspring of hybrids in which 
several differentiating characters are associated. — Two ex- 
periments were made with a considerable number of plants. 
In the first experiment the parental plants differed in the 
form of the seed and in the color of the albumen. Experi- 
ments with seed characters give the results in the simplest 
and most certain way. 

Experiment 1 . — Seed parent = round seeds (R) and 
yellow cotyledons (F). Both dominant and hence their 
symbols are expressed as capital letters. Pollen parent 
= angular seeds (r) and green cotyledons (y). Round 



172 Plant-Breeding 

yellow (RY) X angular green (ry) = RrYy appearing as 
round and yellow in Fi. 

Gametes of Fi = RR, Ry, rY, and ry. 

Visible types oi F^ = 9 (apparently) RY, 3 Ry, 3 vY, 
and 1 ry. 

The following were actually found by Mendel in F2: — ■ 

RY, round and yellow, 315. 

rY, angular and yellow, 101. 

Ry, round and green, 108. 

ry, angular and green, 32. 
These figures stand approximately in the ratio of 9 RY : 
3 rF : 3 Ry : 1 ry, but these forms, which appeared to be 
only four classes, were found in the next generation to be 
made up of nine really different classes. 

From the round yellow seeds (apparently RY) there 
were obtained in the next year : — 

1. RY, round and yellow seeds, 38 

2. RYy, round, yellow and green seeds, 65 

3. RrY, round, yellow and angular seeds, 60 

4. RrYy, round, yellow and green angular, yellow 
and green, 138 

From the round and green seeds (apparently Ry) were 
obtained : — 

5. Ry, round and green seeds, 35 

6. Rry, round angular and green seeds, 67 
From the angular and yellow seeds (apparently rY) 

were obtained : — 

7. rY, angular and yellow seeds, 28 

8. rYy, angular and yellow-green seeds, 67 
From the angular and green ry seeds were obtained : — 

9. ry, angular and green seeds, 30 



Heredity ' 173 

Compare this carefully with problem 4 with special 
reference to the actual counts as compared with theo- 
retical ones. 

The offspring of the hybrids appeared, therefore, under 
nine different forms, some of them in very unequal num- 
bers. When these are collected and coordinated, we 
find : — 

38 plants with the sign RY. 

35 plants with the sign Ry. 

28 plants with the sign rY. 

30 plants with the sign ry. 

65 plants with the sign RYy. 

68 plants with the sign rYY. 

60 plants with the sign RrY. 

76 plants with the sign Rry. 
138 plants with the sign RrYy. 

The whole of the forms may be classed into three essen- 
tially different groups. The first includes those with 
the signs RY (or RRYY, as previously designated — it is 
not necessary, however, to repeat the letters), Ry, rY, and 
ry ; they possess only constant characters and do not vary 
again in the next generation. Each of these forms is 
represented, on the average, thirty-three times. 

The second group includes the signs RYy, RrY, Rry; 
these are constant in one character and hybrid in another, 
and vary in the next generation only as regards the 
hybrid character. Each of these appears, on the average, 
sixty-five times. The form RrYy occurs 138 times; it 
is hybrid in both characters and behaves as do the hybrids 
from which it is derived. 



174 Plant-Breeding 

If the numbers in which the forms belonging to these 
classes appear, be compared, the ratios of 1,2, and 4 are 
evidently unmistakable. The numbers 32, 65, 138 present 
very fair approximations to the ratio numbers of 33, 66, 132. 

The developmental series consists, therefore, of nine 
classes of which four appear therein always once and are 
constant in both characters; the forms RY, ry resemble 
the parental forms, the two others present combinations 
between the conjoined characters R, r, F, y, which com- 
binations are likewise possibly constant. Four classes 
appear always twice, and are constant in one character 
and hybrid in the other. One class appears four times, 
and is hybrid in both characters. Consequently the off- 
spring of the hybrids, if two kinds of differentiating char- 
acters are combined therein, are represented by the ex- 
pression RY — Ry — rY — ry — 2 RYy — 2 rYy — 2 RrY 

— 2Rry — 4:RrYy. 

This expression is indisputably a combination series 
in which the two expressions for the characters R and r, 
y and Y are combined. We arrive at the full number of 
the classes of the series by the combinations of the ex- 
pressions. 

The following, quoted from East, has reduced the 
above to a mathematical expression : ''The numerical rela- 
tions found are approximately the following series : AB, 
Ab, aB, ah, 2 ABb, 2 aBb, 2 Aab, 2 AaB, and 4 AaBb. This 
is really a combination by multiplication of the two series 
(A — 2Aa — a) x {B — 2 Bb — b) = AB — Ab — aB 

— ab — 2 ABb — 2 aBb — 2 Aab — 2 AaB — 4 AaBb. 
The two pairs of characters behave independently of each 
other and as if chance only governed their combinations. 



Heredity 



175 



Moreover, three pairs of contrasted characters were found 
to behave in exactly the same manner, the number of 
forms found being what would theoretically be expected 
if the above product were multiplied by another series 
represented by C — 2 Cc — c. 

''These results can be reduced to still simpler terms, as 
is shown in the following table. Let N represent the 
number of pairs of contrasted characters in the parents. 
When they are crossed the second generation, when self- 
fertilized, shows visible differences of 2 to the nth power. 
These visibly different classes actually contain 3 to the 
nth power different classes, the phenomena of dominance 
obscuring part of them. Finally, when crossing to secure 
combinations of n characters, we must have 4 to the nth 
power number of individuals, to be theoretically certain 
of at least one individual in each class. 

Mendel's Law of Inheritance of Unit-characters 



No. OF Pairs 
OF DiF. BE- 
TWEEN Parents 



No. OF VISIBLY 

DiF. Classes 
Each cont. One 
Pure Individual 



2n 

2 

4 

8 

16 

32 

64 



No. OF Actual 

Classes Both 

Pure and Hybrid 



3n 

3 

9 

27 

81 

243 

729 



Smallest No. Offspring, 

allowing at least One to 

A Class 




An 
Experimentally 
tested by Men- 
del for peas 

Calculated 



A is substituted for R, a for r, B for T, and b for t, and 
instead of writing AA and aa in the series, one of the 
letters is dropped." 



176 



Plant-Breeding 



a, 

U 

W 
O 

w 



o 
Q 

w 

H 

•J 
111 

o 
O 

W 
% 






m 
Eh 



o 



" I 

r '^ 

W « 

& fe. 

« o 

a <> 

o J 

^^ 

w 3 

H ^ 

^ 2 

^ a 

93 hA 

H 

<: 2: 



Oi 

o 

— I o 

o 

o 



1—1 CO 

00 00 

^ CO Q =2 

o 2 "^ 
o o 



00 
CO TfH lo 

o o '^^ o 
o o o 

c5 (5 CD 



o X CO t^ 

.— I lO ■* lO 

O iX) -^ O CO O (N 

O O CO O CN O 

o o o ^ o 



Tfi CO 1^ CO 

rHTjIt^OOOOCO^OO 



o 
d 



r^ c^^ -r" Xi T* '-' o 



o 
d 



O (M 

d 



o o 



o 



(M CO 



^•^s^s^g 



o c5 



O 05 



CO o)^(M=^r-it^^^o;^§ 
d d d d d 



C5 C5 Tjl 1— I 00 05 

0-<^!>Ot^OiOt005COt^rt<I>00 
»0 ^ --H XI (M CO CO '^ >0 CO 00 OJ O) fT-l 



LO v^ C5 
(M '^ O 



«o 



^ 



CO (M --• 



c^ ^; c^i '": ^o "^ '^ ^ 

I— I I— ( o o 



0»OcOiO'-'COtO'!*<OX 
lO X Tti O t^ lO rt^ CO (M.-I1-H 

Cq ,— I r-( .—I 



o 
o 



o 
o 



lo 
(M 



Ci 






CO 



o 
x 



CO 



rH fO 

lO 1:0 

Oi-HO'— lO"— '(M'-H'-Hi— (COl-Ht-l— ICO'— lOi— It^rHlO 
Ot^lO^COCS|r-li-li-l 



<^ o 

H • 

o o 






iM 


'^^ 


X 





(M 


■* 


1—1 


CO 





Ol 





I— 1 


(>< 








T— 1 


04 









b <J 



U 





ao 
























K 


Bh 





»— 1 


fl 


CO 


■* 


10 


CO 


i> 


X 


Oi 





« 


<! 






















"— ' 


H 


CM 

























Heredity 177 

Results involving three pairs of characters (trihyhrid) . — 
When three allelomorphic pairs are concerned, the num- 
ber of forms in the second and subsequent generations is 
greatly increased. For illustration, let us take a hypo- 
thetical case. Suppose we cross together a tomato having 
red fruit, dwarf vine, and hairy stems and leaves (the 
latter is hypothetical) with a variety having yellow fruit, 
tall vine, and smooth stems. Their formulae would be as 
follows, using capitals again to represent dominant units 
and small letters to . represent recessive units : red, 
dwarf, hairy (RtH) x yellow, tall, smooth (rTh) = red, 
tall and hairy (in appearance) RrTtHh. F^ generation 
will be as shown in table on page 178. 

In order to get a better understanding of the probable 
union of gametes of various kinds of crosses, the student 
should carefully master the method of squares, always 
having in mind that the use of formulae is only a con- 
venient method of representing plants. Each square 
represents a plant. (See methods as already outlined on 
page 169.) Capital letters will be used for dominant 
units and small letters for recessives as formerly. Plants 
having as their formulae large and small of any letter, i.e. 
Rr, are hybrids (heterozygous) for that character, and those 
in which the letters are the same, i.e. RR, are pure (homo- 
zygous) for that character. 

It will be seen that when three pairs of characters are 
involved, at least 64 squares are necessary to allow for 
the theoretically possible number of combinations to be 
formed. A very careful study of the table will show that 
there are produced 8 visible types (2") with proportions 
as follows : 27 Red Tall Hairy, RTH ; 9 Red Tall smooth, 

N 



178 



Plant-Breeding 



Pollen-grains 



CO 

W 
o 

I 

o 
o 





RTH 


RTh 


RtH 


Rth 


rTH 


rTh 


rtH 


rth 




RR 


RR 


RR 


RR 


Rr 


Rr 


Rr 


Rr 


RTH 


TT 


TT 


Tt 


Tt 


TT 


TT 


Tt 


Tt 




HH 


Hh 


HH 


Hh 


HH 


Hh 


HH 


Hh 


RR 


RR 


RR 


RR 


Rr 


Rr 


Rr 


Rr 


RTh 


TT 


TT 


Tt 


Tt 


TT 


TT 


Tt 


Tt 




Hh 


hh 


Hh 


hh 


Hh 


hh 


Hh 


hh 


RR 


RR 


RR 


RR 


Rr 


Rr 


Rr 


Rr 


RtH 


Tt 


Tt 


tt 


tt 


Tt 


Tt 


tt 


tt 




HH 


Hh 


HH 


Hh 


HH 


Hh 


HH 


Hh 


RR 


RR 


RR 


RR 


Rr 


Rr 


Rr 


Rr 


Rth 


Tt 


Tt 


ft 


tt 


Tt 


Tt 


tt 


tt 




Hh 


hh 


Hh 


hh 


Hh 


hh 


Hh 


hh 
rr 




Rr 


Rr 


Rr 


Rr 


rr 


rr 


rr 


rTH 


TT 


TT 


Tt 


Tt 


TT 


TT 


Tt 


Tt 




HH 


Hh 


HH 


Hh 


HH 


Hh 


HH 


Hh 


Rr 


Rr 


Rr 


Rr 


rr 


rr 


rr 


rr 


rTh 


TT 


TT 


Tt 


Tt 


TT 


TT 


Tt 


Tt 




Hh 


hh 


Hh 


hh 


Hh 


hh 


Hh 


hh 


Rr 


Rr 


Rr 


Rr 


rr 


rr 


rr 


rr 


HH 


Tt 


Tt 


tt 


tt 


Tt 


Tt 


tt 


tt 




HH 


Hh 


HH 


Hh 


HH 

rr 


Hh 


HH 


Hh 


Rr 


Rr 


Rr 


Rr 


rr 


rr 


rr 


rth 


Tt 


Tt 


tt 


tt 


Tt 


Tt 


tt 


tt 




Hh 


hh 


Hh 


hh 


Hh 


hh 


Hh 


hh 



Note. It must be remembered that these are different visible types 
and not actual types. For example, the 27 which appear as RTh are 
not all alike, their identity is obscured of dominance. 



Heredity 179 

RTh ; 9 Red dwarf Hairy, RtH ; 9 yellow Tall Hairy, rTH ; 
3 Red dwarf smooth, Rth ; 3 yellow Tall smooth, rTh ; 
3 yellow dwarf Hairy, rtH ; and 1 yellow dwarf smooth, 
rth. Of course most of the visible types are multiple, 
containing both pure and hybrid forms. The number of 
actually different types is 27 (3") . 

Incomplete dominance. — It was stated previously that 
dominance is due to an unequal potency between the 
unit-characters associated in a cross, the dominant unit 
being '' stronger" and covering up the weaker unit in the 
Fi generation. 

This is not always the rule, by any means. There are 
various degrees of equiUbrium between the opposed 
units : if one is much stronger than the other, complete 
dominance occurs ; if they are of equal potency, we 
have a form in the first generation which is intermediate 
between the two parents. This intermediacy may 
lean to one parent or the other in proportion to their 
strength. 

When intermediacy exists, the mendehan ratios are 
somewhat modified. Instead of having 3 : 1 ratio, we 
have a 1 : 2 : 1, in which the 2 represents the heterozygous 
or intermediate forms and the Ts represent the homo- 
zygous forms. 

If we are concerned with more than one allelomorphic 
pair, complete dominance may occur in certain units and 
intermediacy or incomplete dominance in others. 

The commercial carnation is a heterozygous form which 
is an intermediate between a single type and a type 
which in commerce is called a ''bull-head" or a ''buster." 
This latter is exceedingly double. When the hybrid 



180 Plant-Breeding 

commercial types are self-fertilized, they produce progeny 
in the approximate ratio of 1 single : 2 commercial doubles : 
1 double-double or bull-head (Fig. 45). 




Fig. 45. — Hybrid carnation (center) between a single and a burster, 

showing intermediacy. 

The hybrids between a large, apple-shaped tomato 
and a small, pear-shaped one are intermediate between 
the parents in the first generation, as has already been 
noted. In all probabiUt}^ there are represented in the 
above characters more than one unit. Emerson has 
made similar observations in beans, gourds, and maize, 
Locke in maize, and Castle in rabbits. 

''While it is not uncommon," says Spillman, ''for a 
character to be dominant or recessive in a cross, it is 
seldom that dominance is absolute. The presence of the 
recessive characters can easily be detected, and in some 
cases very easily. Thus in the cross between bearded 



Heredity 181 

and smooth wheat the hybrids usually show a slight tend- 
ency to be bearded. Likewise, the cross between horned 
and polled cattle may have scars (hornlessnessis dominant). 
It frequently happens that instead of either of two opposite 
characters being dominant, we get a form intermediate 
between the two parent forms. Thus, in the cross be- 
tween long-headed wheat and the short-headed club 
wheats of the Pacific Coast, the hybrids have heads of 
intermediate length, though they are much more Hke 
club wheat than they are like the ordinary kinds, so that 
the club character is at least partially dominant. In cer- 
tain crosses between red-flowered and white-flowered 
ornamental plants the hybrids are pink." 

Presence-and-absence hypothesis. — The phenomena of 
mendelian inheritance may be explained in one of two 
ways : first, the presence of a definite substance in the 
germ cells of both parents representing each unit-character 
in the allelomorphic pair, and, second, the ''presence-and- 
absence" hypothesis. The latter assumes that what 
appears to be a pair of characters is really the presence 
and absence of a single character. 

Examples of mendelian inheritance due to the presence- 
and-absence of a single unit. — ^ Red flowers may be 
due to the presence of red, and white flowers to its 
absence. 

The wrinkled pea owes its character to the absence of 
something which the round pea possesses. Darbishire 
has found in the round pea that all of the sugar has been 
converted into starch, while only a part of it has been 
thus converted in the wrinkled pea and the wrinkUng is 
primarily due to the escape of the water from the solu- 



182 Plant-Breeding 

tion of sugar left over after ripening, and, consequently, 
in the last resort due to the absence of that which completes 
the conversion of the sugar into starch or, at any rate, 
to an insufficiency in the quantity of that substance, 
whatever it is. The round pea has the full share of this 
substance, the wrinkled pea an insufficient one. Some- 
thing is absent from the wrinkled which is fully present 
in the round. 

The same author applies the presence-and-absence 
hypothesis to another pair of characters in peas, the 
color of the cotyledons. The two characters which meet 
the eye are yellow and green. But the matter is not 
so simple as this. Bunyard has shown that there is a 
yellow and a green pigment both in the yellow and in 
the green cotyledon. When both are present at 
the same time, as in the ripe but still moist pea, 
the green masks the yellow. All peas, both yellow 
and green varieties, are green when they are eaten. 
Just as cooks think that all peas are round, so they 
think that all peas are green. It is only gardeners who 
sow and harvest them who know the distinction between 
yellow and green. 

The ripe but still moist cotyledons of both yellow- and 
green-seeded varieties are, therefore, green. The yellow 
kinds become yellow as they ripen ; the green do not 
change color during this process. The yellowing of the 
former is brought about by the gradual fading and dis- 
appearance of the green pigment, which thus leaves the 
yellow pigment (which is present in both kinds) exposed. 
The successive stages in the fading of the green can be 
easily observed. The simultaneous presence of both 



Heredity 183 

green and yellow pigment in yellow and in green peas 
has also been demonstrated. 

Green-seeded varieties therefore contain two pigm,ents 
in their cotyledons, a yellow and a green ; neither of them 
fades during the process of ripening, and inasmuch as 
the green masks the yellow, the ripe seed is green. Yellow- 
seeded varieties also contain the same two pigments, but 
the green fades in the process of ripening, so that the 
ripe seed is yellow. This fading of the green pigment in 
the yellow pea is supposed to be brought about by the 
presence of some substance which is absent from the green 
pea. Similarly, when the apparent absence of a character 
is dominant, as in the case of dominance of hornlessness in 
cattle and of white color in swine, there is believed to be 
present an inhibiting factor or ''inhibitor" which pre- 
vents the formation of the black pigment. In other 
words, it is the presence of the inhibitor (causing white) 
over its absence (black) which explains the phenomena of 
the dominance of white over black. 

It is not the dominance of an absent factor, but the 
presence of an unseen inhibitor, which reacts upon the 
otherwise visible character, causing it to disappear. 

Let us now consider another type of cause which may 
be explained on the basis of the presence-and-absence 
hypothesis. The heredity of the combs of fowls has been 
carefully studied by Bateson, Davenport, Punnett, and 
others. The latter gives an excellent description ^ of this 
on the presence-and-absence hypothesis. 

Four types of combs are recognized ; namely, rose, pea, 
walnut, and single. (See Fig. 46.) 

1 Punnett, " Mendelism," pp. 35, 36. 



184 



Plant-Breeding 




Rose and pea combs behave as simple dominants to 
single comb, segregating in the F2 generation in the nor- 
mal 3 : 1 ratio. What happens when the two dominants 
are bred together? It was found that a third type ap- 
peared as an Fi hybrid, the so-called walnut comb. 
When these Fi hybrids were bred inter se, four types of 

combs were found 
among the F2 prog- 
eny ; namely, walnut, 
pea, rose, and single 
in the approximate 
ratios of 9:3:3:1 
respectively. What 
is the explanation 
of this unusual phe- 
nomenon ? 

We are evidently 
concerned with two 
allelomorphic pairs 
of characters, which 
are the presence-and- 
absence of rose comb 
(R) and the presence-and-absence of pea comb (P). 
As suggested by Punnett, let us denote the rose comb 
by RRpp (containing the presence of rose and the 
absence of pea) and the pea comb by rrPP. When these 
are crossed together, the zygote RrPp results. This 
differs from either and has a walnut comb. When these 
Fi hybrids are crossed together (RrPp x RrPp), the fol- 
lowing results may be graphically expressed in the series 
of squares : — ■ 





Fowls' combs : A, pea ; B, rose ; 
C, single ; D, walnut. 



Hereditij 



185 



RP 



Spermatozoa 
RV rP 



rp 



RP 



Rp 



< 
> 
O 



rP 



rp 



RP 
RP 

Walnut 


RP 

Rp 

Walnut 


RP 

rP 

Walnut 


RP 

rp 
Walnut 


RP 

Rp 

Walnut 


Rp 
Rp 

Walnut 


Rp 

rP 

Walnut 


Rp 
rp 
Rose 


RP 

rP 

Walnut 


Rp 

rP 

Walnut 


rP 
rP 
Pea 


rP 
rp 
Pea 


RP 

rp 
Walnut 


Rp 
rp 
Rose 


rp 
rP 
Pea 


rp 

rp 

Single 



Diagram to illustrate the nature of the F2 generation from the cross of 
rose comb X pea comb. (After Punnett.) 

All the resulting zygotes containing both rose and pea 
(RP) will be walnut ; those containing rose only {R) and 
not pea (p) will be rose and those containing pea only (P) 
and not rose (r) ^vill be pea-combed. But all individuals 
containing neither rose nor pea will have single combs. 
This was found to be a pure recessive and to breed true. 
The character of singleness seems to underUe all the types 
of comb and appears whenever allowed to do so by the 
absence of something representing the other kinds. 

Mendelian inheritance of color. — Colors of plants or 
animals are generally very complex and often consist of 
many units of different kinds. Very rarely a certain color 
may be said to be due to a single unit acting alone. A 
knowledge of the kinds of color and the constitution of 
each is necessary to understand their inheritance. 



186 Plant-Breeding 

1. White is due to the absence of pigment, and to the 
reflection of light from the cells. 

2. Green color is caused by the presence of a green 
pigment in the chlorophyll. 

3. Yellow, cream, and related colors are due to a 
yellow pigment either associated with green in the chloro- 
plasts or found alone in the chromoplasts, generally the 
latter. Yellow may sometimes come from the cell-sap. 

4. Red color may, under certain circumstances, be due 
to the presence of that pigment in the chromoplasts, but 
it is ordinarily a cell-sap color. 

5. Most of the remaining colors, purple, blue, generally 
red, pink, etc., are due to pigments in the cell-sap. 

6. Many of the colors and shades found in flowers 
are the result of both plastid colors and cell-sap colors 
acting together in various amounts. 

7. Certain of the denser plastids or cell-sap colors may 
cover up the more delicate colors so that they cannot be 
seen. 

8. Finally, the color in the cell-sap may be due to 
the relative presence of a non-nitrogenous and chemical 
substance anthocyanin. This is blue in an alkahne and red 
in acid reacting cell-sap, and, under certain conditions, 
also dark red, violet, dark blue, and even blackish blue. 
Anthocyanin can be obtained from the supersaturated 
cell-sap of a number of deeply colored parts of plants in 
a crystalline or amorphous form. Blood-colored leaves, 
such as those of the Copper Beach, owe their characteris- 
tic appearance to the united presence of green chlorophyll 
and anthocyanin. The different colors of flowers are due 
to the varying color of the cell-sap, to the different dis- 



Heredity 187 

tribution of the cells containing the colored cell-sap, 
and also to the combinations of dissolved coloring 
matter with the yellow, orange, and red chromoplasts 
and the green chloroplasts. There is occasionally found 
in the cell-sap a yellow coloring matter known as xan- 
thein ;• it is nearly related to xanthophyll, but soluble in 
water. 

Thus we see the plant colors are not always unit-charac- 
ters, such as hairiness, glabrousness, and the like. Certain 
colors found in plants, purple flowers, for example, are 
the result of the union of certain other pigments. These 
pigments are produced by definite units in the gametes. 
Color inheritance thus becomes very complicated as the 
results of certain crossings indicate. 

White flowers in F2 from red X cream. — Bateson points 
out a typical case of the paradoxical appearance of white- 
flowered individuals in the Fi from the cross of a sap- 
colored variety with a variety having cream-colored 
flowers. For example, in sweet peas or stocks, when a 
red-flowered type is crossed with a cream, i^i is red with- 
out any cream color. F^ consists of 9 without cream, 3 
reds with cream, 3 whites, 1 cream. 

The red-flowered variety consists of red sap color only 
and the cream variety of yellow plastids only. These 
are inherited separately in the hybrids. The 9 reds of 
the F2 hybrids have a much brighter red color than the 
red-creams. In the latter the red is diluted by the yellow 
plastids. 

When the allelomorphs are correctly distinguished, the 
significance of this series is obvious. The operations may 
be shown in tabular form, thus : — 



188 



Plant-Breeding 



Parents . 
Allelomorphs 



F2 



Red variety X 

Red sap (D) 
Colorless corpuscles (D) 



Cream variety 
Colorless sap (r) 
Yellow corpuscles (r) 



Red sap 

Colorless corpuscles 



III I 

Red sap Red sap Colorless sap Colorless sap 

Colorless Yellow Colorless Yellow 

corpuscles corpuscles corpuscles corpuscles 

Appearance 9 red 3 red-cream 3 white 1 cream 



The ratio 9:3:4- — The F2 ratio, 9 : 3 : 4, is one which 
very frequently occurs in mendelian analysis. For ex- 
ample, as Tschermak found, when a pink-and-white 
flowered eating pea {Pisum, sativum) is crossed with a 
white-flowered type, Fi is often the original purple-flowered. 
Then F2 wAX be 

9 purple : 3 pink and white : 4 white. 

In this case the factor for purple is evidently brought in 
by the albino. The latter contains the presence of 
purple, which needs a factor from the other parent to 
bring it out, and the absence of pink and white. The 
other parent contains the presence of pink and white 
and the absence of a factor for purple. All that is essen- 
tial for the production of the ratio in Fi is that Fi should 
be heterozygous for two factors, of which one is percep- 
tible whenever present, while the other needs the presence 
of the first in order that its own effects may be mani- 
fested. 

Emerson^ s experiments with heans. — By crossing self- 
colored varieties of beans with white varieties, Emerson 



Heredity 189 

obtained in the Fi generation, 65 mottled. In F2 genera- 
tion there were 113 mottled, 52 self-colored, and 70 
white, that is, in the ratio of 6.45 : 2.97 : 4 instead of 
9:3:4. 

In the F3 generation he secured the following results : — 

1. All white seeds produced white seeds. 

2. 7 mottled gave 22 mottled, 19 self-colored, 11 white. 

3. 2 mottled yielded 13 mottled, 13 self-colored. 

4. 4 mottled bore 5 mottled, 5 white. 

5. 2 mottled produced 6 mottled. 

6. 5 self-colored gave 63 self-colored. 

7. 9 self-colored yielded 80 self-colored, 29 whites. 
For the purpose of explaining the above, Emerson adopted 
the formula of ShuU. 

1. P and p for the factor presence and absence of pig- 
ment. 

2. M and m for the factor presence and absence of 
mottUng. 

3. Pm = self-colored. 

4. pM = white. 

5. PM = mottled. 

Thus he considers a self-colored variety containing the 
factor for pigment and having no factor for mottUng. 
The white variety lacks the factor for pigment, but has 
the factor for mottling. The mottled form is originated 
by the presence of two factors, for the pigment and 
mottling. 

If we follow these formulae, we must confer to the F\ 
generation the following gametic composition, PpMm, 
since Fi hybrids will produce 9 mottled, 3 self-colored, 
and 4 white for the F2 generation as seen on page 190 : — 



190 



Plant-Breeding 



PM 



Pollen-grains 
Pm pM 



pm 



PM 



Pm 






pm 



PM 

PM 

Mottled 


Pm, 
PM 

Mottled 


pM 

PM 

Mottled 


pm 

PM 

Mottled 


PM 

Pm 
Mottled 


Pm 
Pm, 
Self 


pM 

Pm 

Mottled 


pm, 
Pm 
Self 


PM 

pM 

Mottled 


Pm 

pm 

Mottled 


pM 

pM 

White 


pm 

pM 

White 


PM 

pm 
Mottled 


Pm 

pm 
Self 


pM 

pm 
White 


pm 

pm 

White 



The ratio of 6.45 : 2.97, instead of 9:3:4, seems to be 
chiefly due to the paucity of number treated for hybridi- 
zation. Doubtless it is no small importance to study 
the ratio of offspring in F^ in the Ught of the theoretical 
deduction. But here again the insufficient number of 
seeds informs us of its inadvisibility. 

In conclusion Emerson says: "The result of most of 
my own experiments might be explained as due to the 
mendehan behavior of an allelomorphic pair, Mm presence 
and absence of motthng, M being visible only in the pres- 
ence of P." 

Colored forms from white X white and the 9 : 7 ratio. — ■ 
In the case of the sweet peas, Bateson has shown that the 
formation of color in the flowers can be proved to depend 
on the coexistence of two complementary factors in the 
individual. 

He says that the first indication of this phenomenon 



Heredity 191 

was found in the fact that two plants, each totally devoid 
of color in the flowers and stems and each breeding true 
to albinism may, when crossed together, give purple 
flowers in Fi. The two white parents each contain a 
factor which, alone, is incapable of forming color. Each 
of these factors is independently transmitted in gameto- 
genesis, and thus in F2 the ratio of colored individuals to 
whites is 9 : 7. This proportion depends on the fact that 
a series of 16 individuals is necessary to exhibit all the 
possible combinations of germ cells, for, as in any example 
of hybridization involving two pairs of allelomorphs, 
there will be four types of female cells and four types of 
male cells produced by Fi. Of these sixteen individuals, 
9 will contain both the dominant or present factors, while 
of the remaining seven individuals, 3 will contain one 
dominant, 3 will contain the other, and 1 will contain 
neither. There will, therefore, be 9 which are colored 
and 7 which are albino. In the diagram (p. 192) C 
and R are the symbols representing the two comple- 
mentary factors, c and r being their respective allelomor- 
phic absences. 

Absence factors. — It may be well for us in this connection 
to touch upon the different conceptions of several investiga- 
tors on such characters as cannot be seen without resorting 
to breeding tests. Tschermak considers the appearance of 
motthng in Fi between a white and self-colored varieties 
due to the presence of mottling in a latent condition in 
the self-colored variety. Latency in his view is inactivity. 
Shull often speaks of latent characters, but latency, 
according to him, means invisibility and not dormancy or 
inactivity. 



192 



Plant-Breeding 
Pollen-grains 





CR 


Cr 


cR 


cr 




CR 


Cr 


cR 


cr 


CR 


CR 


CR 


CR 


CR 


• 


Colored 


Colored 


Colored 


Colored 




CR 


Cr 


cR 


cr • 


2 Cr 


Cr 


Cr 


Cr 


Cr 




Colored 


White 


Colored 


White 


1 

o 


CR 


Cr 


cR 


cr 


cR 


cR 


cR 


cR 




Colored 


Colored 


White 


White 




CR 


Cr 


cR 


cr 


cr 


cr 


cr 


cr 


cr 




Colored 


White 


White 


White 



Composition of the 9 colored and 7 albino offspring in F2 from the 
cross between the albino Cr with albino cR, showing the ratio 9 colored : 
7 albino. 

On the other hand, Bateson advocates the undesir- 
ability of using such a terminology. He scorns the idea 
that there is latency of mottling or red in the white forms. 
Certain factors may be present which are absolutely 
necessary for the production of such pigments, but this 
fact does not lead us to contend that there are those colors 
latent. He emphasizes stating that ^'sulphate of copper 
is blue and chloride of copper is green, but it would be 
incorrect to speak of blue as latent in sulphuric acid, or 
of green as latent in hydrochloric acid." 

Hurst seems to have difficulty to perceive a factor for 
absence. He brings forth three distinct views : — 

1. The absence factor may be a concrete one, literally 
representing absence. 



Heredity 193 

2. It may be nothing but presence in a latent state. 

3. There may not be such a factor as the absence 
factor. 

Of the three proposed, the first seems to be, Hurst 
remarks, the simplest, but it is difficult to realize and 
understand how such an absence factor is originated. 
Furthermore, he says: ''There are many cases where 
the factor for presence is in a latent condition." The 
third explanation meets an objection in the fact that there 
is no pairing of factors in cross-breeding. Consequently, 
it follows that, according to this view, it is impossible to 
explain the phenomenon of segregation. 

Mutations resulting from mendelian segregation and re- 
combination. — It is very probable that many mutations 
which appear suddenly and remain constant are the result 
of mendelian segregation and recombination. If many 
unit-characters are involved, it is easily perceived how 
certain combinations of these would produce plants 
of unusual appearance which will be homozygous and 
breed true. Reference to Table I, p. 176, will show the 
great possibilities of obtaining apparently new characters 
by new combinations of old ones. It will be noted that 
when as many as 10 allelomorphs are involved, and this 
does not seem to be an impossible number, there is the 
possibihty of producing 1024 different visible types. 

Mutations which mendelize are co7istant. — The effect 
of swamping of mutations by crossing is prevented be- 
cause of their continued identity due to the purity of the 
germ-cells which represent them. 

Mutations may be due to three things : (a) the ac- 
quisition of one or more new characters, (6) the loss of 
o 



194 Plant-Breeding 

one or more characters, and (c) recombination of existing 
characters. 

If the mutation is due to the addition of a new char- 
acter and it remains constant, there must be present in 
its germ-cells some unit to represent that new character as 
there was in the gametes of the parent which produced it. 
Likewise, if a character is lost, its germinal potentiality 
must have become lost or entered into a latent condition. 

If mutations of these types are crossed, the new gametic 
representatives or absences in the case of a lost character 
become pure in the germ-cells and reappear in the next 
generation. Hence they are not lost. 

If the mutation has a hybrid beginning and is due to 
an unusual combination of characters, this condition can- 
not be lost, as this certain combination which has once 
occurred will reproduce true if it is homozA^gous, or if not, 
it having occurred once may appear again through a like 
combination of unit-characters even though crossing and 
amphimixis may have taken place. 

Mendelism in wheat. — As a specific example of evident 
mendelian results, W. J. Spillman, agriculturist of the 
Department of Agriculture, here explains some of his ex- 
periments with, wheat. ^ Mr. Spillman independently dis- 
covered numerical results, before the knowledge of the 
mendelian experiments had become generally kno\\Ti. 

''The photograph (Fig. 47) shows three generations of 
one of my hybrid wheats. Of the three heads in the 
upper row, the left-hand one is the male parent (variety 
Valley) ; the right-hand one is the female parent (variety 

1 Published in fourth edition of this work, 1906; and here reproduced 
nearly entire for its historical as well as for its plant-breeding value. 



Heredity 



195 




Fig. 47. — Three generations of hybrid wheat: A 1 = male parent, 
A 2 = the hybrid, A 3 = female parent : B 1-6 = the progeny of A 2 ; 
C 1 = progeny of B 1 , C 2-4 = progeny of B 2, C 5 = progeny of B 3, 
C 6 and 7 = progeny of B 4, C S-13 = progeny of B 5, C 14 and 15 
= progeny of B 6. The results in the fourth generation, available 
too late to include in the photograph, indicate that B 2 and B 3, 
while not always separable on external appearances, are absolutely 
different, the one being hybrid, the other pure. 

Little Club); and the middle one is the hybrid. The 
second row shows the second generation, and the third 
row the third generation. Of the six types in the second 
generation, the following points are important : Each 



196 



Plant-Breeding 



type was present in a certain proportion, which was ap- 
proximately the same as in thirteen other similar cases, 
and the average of these fourteen cases approximated the 
theoretical numbers called for by Mendel's hypothesis 
of the disjunction of parental characters. The three 
at the left, being bearded, possess a character which 
was latent in the first generation. The fact that the 
beards show in these three indicates that the opposite 
character is absent, and they should therefore remain 
bearded in succeeding generations. That is, they are no 
longer hybrid with reference to this character. It will 
be observed that this was actually the case, for no beard- 
less heads appeared in the progeny of either of these three 
(see lower row, first five heads). The following diagram 
will show the character of each of the six types in row 2. 
In this diagram the letters have the following meanings : — 

B = bearded (written b when latent) . 
S = smooth (not bearded). 
L = long heads. 
C = Club heads (short). 

/ = Intermediate in length of head. (The hybrid was 
intermediate in this respect.) 

Parents First Generation 



BL 



Sbl 



sc 



Second Generation 


1 


BL 


2 


BI 


1 


BC 


2 


SbL 


4 


Sbl 


2 


SbC 


1 


SL 


2 


SI 


1 


SC 


16 





Heredity 197 

''This diagram shows the nine types called for by 
Mendel's theory. Of these, BL, BC, SL, and SC are 
no longer hybrids — at least they have no latent char- 
acters, and vnW therefore reproduce true to seed. Of the 
remaining five types, BI and SI are hybrid only ^^dth 
reference to length of head, and SbL and ShC only with 
reference to beards; while Sbl is hybrid with reference 
to both characters, as in the preceding generation. 

''It will readily be seen that the types BL and BC can 
be separated from the others even by external appearances, 
and obtained in a pure state. BL is the type showTi at 
the left in the second row in the picture, and all its prog- 
eny was like it, showing that it conformed to theory. BC 
is the type sho^vn at No. 3 in the second row of heads ; 
being pure, it should reproduce itself true to tjq^e, which 
it did, with an easily explained exception to be noted be- 
low. The type BI (sho\^^l at No. 2, row 2), being hybrid 
with reference to length of head, should produce again 
all types based on this character, and it did this, as is seen 
in heads 2-4, row 3. Referring again to the above 
diagram, it will be seen that the types SL and SbL cannot 
be distinguished by external characters. SL ^^^ll of course 
reproduce true to type, while SbL will reproduce SL, 
SbL, and BL. Now .SL and SbL being mixed together in 
the selection made in the second generation, we shall find 
a large percentage of SL mixed with some SbL from which 
it cannot be distinguished, and a small percentage of BL 
in the third generation. Heads 6 and 7, row 3, show that 
the types called for actually occurred. Types SI and Sbl 
of the diagram appear alike externally, and were there- 
fore selected together in the' second generation (see head 



198 Plant-Breeding 

5, row 2). Now SI should produce the types SL, SI, 
SC, while Shi should produce all nine types again 
(these nine types can be separated only into six by exter- 
nal appearance). It is therefore seen that the group 
represented by head 5, row 2, should produce all six types 
again. Heads 8-13, row 3, show these types. Types 
SbC and SC of the diagram are alike externally, and were 
hence selected together last year. Of these SC should 
produce only SC, while SbC should produce SC, SbC, and 
BC. But since SC and SbC look alike, the progeny of 
these two types should show only SC and BC. The last 
two heads in row 3 show that this actually occurred. 
''In the single set of heads shown, there were two easily 
explained exceptions to theory. It will be seen that 
heads 2 and 3, row 2, differ only in length ; now the group 
represented by head 2 varied in length from that of 1 to 
that of 3. In separating 2 and 3, it might easily happen 
that some of 3 should be placed with 2. In this case 
the progeny of 3 would show a few heads like 1, and this 
was the case. I have shown in the photograph only the 
heads called for by theory, for it would only lead to con- 
fusion to include the exceptions which would probably 
not have occurred if 2 and 3 of row 2 had been accurately 
separated last year. Again, in the progeny of the group 
represented by head 5, row 2, only five of the six types 
shown (row 3, heads 8-13) were found in this particular 
case, though all six were found in most of the others. 
As the missing type should constitute only 4^ per cent 
of the group, and as it differed from one of the others 
only slightly, it is possible that it was included with the 
related type when the selections were made. 



Heredity 199 

''I have not yet seen the data for the third generation 
of all these wheats, but those which are at hand are 
decidedly interesting. The following are the data for 
the third generation of the cross between Jones Winter 
Fife (male) and Little Club (female). The fife is long- 
headed and has velvet chaff (F) ; the Club short-headed, 
and has glabrous chaff (G). Velvet proved to be domi- 
nant over glabrous and the hybrids were intermediate in 
length. Type I of the second generation included the 
two t}Tpes VL and VgL, since these could not be distin- 
guished by external appearances. Seed of Type I pro- 
duced in the third generation : — 

Percentage of Types 
Plot I = FL ll = GL 

1 87 13 

2 8]_ 29_ 

Theory 83^ IGf 

The figures for the remaining five second-generation types 
are as follows : — 









Type II = 


GL 














Percentage op 


Types 




Plot 








II 






1 








100 






2 








100 






Theory 




• 


100 








Type III = VI 


AND Vgl 






Plot 


I 


II 


III 


IV 


V 


VI 


1 


21 


7 


38 


9 


20 


5 


2 


19 


ii 


38 


12 


15 


41 


Theory 


201 


41 


41f 


8i 


201 


4i 



200 



Plant-Breeding 



Plot 



Type IV = GI 

II IV VI 

28 52 20 

31 47 22 



Theory 




25 


50 


2^ 




Type V = VC 


AND VgC 




Plot 


I 


II 


V 


VI 


1 
2 


2.4 
4.7 


2.6 


80.0 

79.8 


17.6 
12.9 


Theory 




Type VI 


83f 


161 


Plot 




II 




VI 


1 
2 




7.7 




92.3 
100.0 



Theory 



100.0 



"The only departures from theory of any consequence 
in these data are the occurrence of small amounts of 
Types I and II in the progeny of V, and of II in the prog- 
eny of \T. Now, Type V of the second generation 
{VC and VgC) differed from Type III (VI) only in being 
slightly shorter. If a few individuals of III had been 
included in V in separating the types of the second gen- 
eration, we should have the actual result obtained in the 
third generation. Likewise, Type VI of the second gen- 
eration (GC) differed from II (GI) in the same manner. 
Evidently a few plants of II got into the Type VI last 
year, and thus gave the results shown." 

Mendelism smmnarized. — This, in barest epitome, is the 
teaching of Mendel. This teaching strikes at the root 
of two or three difficult and vital problems. It represents 



Heredity 201 

a new conception of the proximate mechanism of heredity, 
although it does not represent a complete hypothesis of 
heredity, since it begins with the gametes after they are 
formed and does not account for the constitution of the 
gametes, nor the way in which the parental characters 
are impressed upon them. This hypothesis focuses our 
attention along new lines, and will arouse more discussion 
than Weismann's h\T)othesis did ; and it will have a much 
wider influence. Whether it expresses the actual means 
of heredity or not it is yet much too earlj^ to say ; but 
this h^-pothesis is a greater contribution to science than 
the so-called ''Mendel Law" as to the numerical results 
of h\'bridization : the hypothesis attempts to explain the 
"law." 

One great merit of the hj^^othesis is the fact that its 
basis is a morphological unit, or at least an appreciable 
unit, not a mere imaginary concept. This unit should be 
capable of direct study, at least in some of its phases. 
It would seem that the mendelian hj^jothesis would give 
a new direction to cytological research. ^ 

It is yet too early to say how far ^lendel's law appUes. 
We shall need to restudy the work that has been done 
and to do new work along more definite lines. There 
are relatively few former results or experiments that can 
be conformed to Mendel's law, because the data are not 
complete enough or not made from the proper point of 
view. We should expect the fundamental results to 
be masked when the plants -^-ith which we work are 

^ See, for example, "A Cytological Basis for the Mendelian Laws," 
Bull. Torr. Bot. Club, 29, 657 (1902), by W. A. Cannon; and other 
papers of this kind. 



202 Plant-Breeding 

themselves unstable, when cross-fertilization is allowed 
to take place, or when the pairs of contrasting characters 
are very numerous and very complex. 

Application to plant-breeding. — The wildest prophecies 
have been made in respect to the appUcation of Mendel's 
law to the practice of plant-breeding, for the mathe- 
matical formulae express only definiteness and precision. 
Unfortunately, the formulae cannot express the indefinite- 
ness and the unprecision which even Mendel found in his 
work. The greatest benefit of Mendel's work to the 
plant-breeder will be in improving the methods of ex- 
perimenting. We can no longer be satisfied with mere 
''trials" in hybridizing: we must plan the work with 
great care, have definite ideals, ''work to a Une," and 
make accurate and statistical studies of the separate 
marks or characters of plants. His work suggests what 
we are to look for. 

The time may come when the hybridizer will be able 
with many plants to make out beforehand plans and speci- 
fications for their breeding and for carrying these through 
with a large degree of exactness. 

The best breeders now breed to unit-characters, for this 
is the significance of such expressions as "avoid breeding 
for antagonistic characters," "breed for one thing at a 
time," "know what you want," "have a definite ideal," 
"keep the variety up to a standard." In certain classes 
of plants the mendelian laws will be found to apply with 
great regularity, and in these we shall be able to know be- 
forehand about what to expect (Fig. 48). The number of 
cases in which the law or some modification of it applies 
is being extended daily, both for animals and plants ; but 



FEMALE PARENT 
Variety — Yellow Plum 



F. HYBRID 



MALE PARENT . 
Variety — Quarter Century 




Height— hiH 

Color — yellow 
Size — small jilitni. 



4^ 



Height— <o/t 

Color — red 

Size — small plum 




Height— dwarf 
Color — red 
Size— small plum 



M^ 



Helzht— tall 

Color — red 

Size — large round 






Height — dwarf 

Color— rcrf 

Size — large round 




Height— ;a« 

Color — red 

Size — intermediate 

F2 HYBRIDS 




Height— <a« 

Color— red 

Size — intermediate 




Height — dwarf 
Color — red 
Size— intermediate 




Height— /aZi 
Color — yellow 
Size — intermediate 




Height— rfifor/ 
Color — yellow 
Size — intermediate 




Height— d war/ 
Color — red 
Size— {arye rOund 




Height— toH 
Color — yellow 
Size — amall plum 




Height— dwarf 
Color — yellow 
Size — small plum 




Height— tall 
Color — yellow 
Size— large round 




"Height— dwarf 
CQlor-yellow 
Size — large round 



Fig. 48. — Mendelism in tomatoes. There were found in a field of F2 
hybrids, the 12 distinct types, ilhistrated above. This redistribution 
of characters illustrates an important economic bearing of Mendel s 
law. 

203 



204 Plant-Breeding 

in practice we shall probably find as many exceptions to 
the formulae as confirmations of them, even though the 
exceptions can be explained, after we fiiid them, by Men- 
del's principles of heredity. 

The probable limits of mendelism in the production of 
new varieties. — It has been said that we shall soon be 
able, as a result of Mendel's discoveries, to predict varie- 
ties in plant-breeding. Before considering this question, 
we must recall the fact that a cultural variety is a succes- 
sion of plants with characters sufficiently marked and 
uniform to make it worth while cultivating in place of 
some older variety. Now and then it may be worth 
while to introduce some new energy or new trend into a 
general lot of offspring by making wholesale crosses, not 
expecting ever to segregate any particular variety or 
strain from the progeny ; but these cases are rare, and the 
gain is indefinite and temporary. So far as our knowledge 
at present goes, we see no warrant for the hope that we can 
predict varieties with any degree of exactness, at least 
not beyond a very narrow effort. Following are some of 
the reasons that seem to argue against the probability 
of useful prophecy of varieties so far as the mende- 
lian results are concerned : (1) We do not know what 
plants will mendelize until we try. (2) Even in plants 
that do not mendelize, one-half of the offspring have 
stable characters. But we cannot predict for even this 
half, for it is impossible to determine beforehand which 
seeds showing dominant characters (and these are three- 
fourths of the offspring) will ''come true." Dominance, 
as we have seen, is of two kinds in respect to its behavior 
in the next generation, — constant and hybrid; and the 



Heredity 205 

hybrid dominance, which is twice as frequent as the 
other, breaks up into constant dominance, hybrid domi- 
nance, and recessiveness. (3) Mendel's law deals pri- 
marily with mere characters, not with a variety or with 
a plant as a whole. Every plant is a composite of a mul- 
titude of characters, and from the plant-breeder's point 
of view there may be as many undesirable characters as 
desirable ones. No plant is perfect ; if it were, there 
would be no need of plant-breeding. The breeders want 
to preserve the desirable characters or traits and elimi- 
nate the undesirable ones ; but under the strict interpre- 
tation of mendelism this may be difficult and perhaps 
impossible. The one egg gamete and the one sperm 
gamete that unite to make the new plant, each contains 
all the alternative parental characters; these various 
characters appear in the offspring, and all that the breeder 
gains is a new combination or arrangement of characters, 
and the undesirable attributes may be as troublesome 
as before. (4) The breeder usually wants wholly new 
characters as well as recombinations of old ones, or he 
wants augmented characters, and these lie outside the 
true mendelian categories. For example, a carnation 
grower wants a four-inch flower, but he has only three- 
inch flowers to work with, and the augmentation of char- 
acters is no part of the original mendelian law. Perhaps 
these augmented and new characters are to be got by 
means of ordinary variation and selection, or other extra- 
crossing means ; but we know, as a matter of fact, that 
augmented characters do sometimes appear in hybrids. 
(5) New and unpredictable characters are likely to arise 
from the influence of environment or other causes, and 



206 Plant-Breeding 

very likely may be recorded in the gametes and vitiate 
the final results. (6) Variability itself may be a unit- 
character and therefore pass over. There is probably 
such a thing as a ''tendency to vary," wholly aside from 
the fact of variation. (7) Many of the plants with which 
we need most to work in plant-breeding are themselves 
eminently variable, and the results, even if there is true 
mendelism, may be so uncertain as to be wholly unpre- 
dictable. (8) Many plants with which we must work 
will not close-fertilize. Some of them are monoecious or 
dioecious. Even if there is gametic purity in such plants, 
the probability is that the fact can be discovered only by 
a long line of scientific experimenting for that particular 
purpose and not by the work of the man who desires only 
to breed new plants. (9) A cultural variety, in any true 
acceptation of the term, is a series of closely related 
plants having a pedigree. It runs back to one individ- 
ual plant, from which propagation has been made 
by seeds or asexual parts. Now, one can never predict 
just what combination of characters any plant will have, 
even though it be strictly mendelian. A person might 
have a thousand hybrids of which no one plant shows any 
two characters in the proportion of 3 to 1 (both seed-char- 
acters may appear in the same pod or in different pods) on 
the same plant, let alone all the characters as 3 to 1 or in 
other definite relation ; and yet the total average numeri- 
cal results might conform exactly to the mendelian law. 
Mendel's law is a law of averages. For example, in ten 
plants of peas, Mendel found the following ratios in respect 
to seed-shape and seed-color. (Similar ratios were found 
for other characters.) 



Heredity 



207 



Shape 


Color 


Shape 


Color 


3.75 




2.27 




4.33 : 1 


3.33 : 1 


3.37 




4.57 




3.66 


1 


2.43 


1 


3.43 




2.80 




2.20 


1 


4.88 


1 


1.90 




2.59 




4.66 


1 


3.57 


1 


2.91 




1.85: 




3.57 


1 


2.44 


1 



Mendel reports one instance in which the ratio in seed- 
shape was 21 to 1, and another of 1 to 1. He also reports 
instances of seed-color of 32 to 1, and 1 to 1. It has been 
said that, because of Mendel's work, we shall be able to 
produce hybrid varieties with the same certainty that we 
produce chemical compounds. Now, a plant is made 
up of many combinations of many units, and these com- 
binations are the results of mathematical chance or prob- 
ability. Of course, when the offspring are numerous, 
all possible combinations are likely to occur; but these 
occurrences are essentially fortuitous. Chemical com- 
pounds are specific entities in which the parts combine by 
necessity with definiteness. The comparison is fallacious 
and the conclusion unsound. 

We must remember that there are whole classes of cases 
of plant-breeding that do not fall under hybridization at 
all. Granting the de Vriesan view that selection is incom- 
petent to produce species from individual fluctuations, it 
is nevertheless well established (and admitted by de Vries) 
that very many of our best cultural varieties have been 
brought to their present state of perfection by means of 
selection ; and by selection they are maintained in their 
usefulness. Selection will always be a most important 
agency in the hands of the gardener and the plant-breeder 



208 Plant-Breeding 

— none the less so now that we have challenged its role 
in the evolution of the plant kingdom. For the time 
being, the new discussions of hybridizations are likely 
to overshadow all other agencies in plant-breeding; but 
selection under cultivation is as important now as it was 
in the days of van Mons and Darwin. 

Conclusion. — Now, in conclusion, what are the great 
things that we have learned 'from these newer studies? 
(1) In the first place, we have been brought to a full stop 
in respect to our ways of thinking on these evolution 
subjects. (2) We are compelled to give up forever the 
taxonomic idea of rigid species as a basis for studying the 
process of evolution. (3) The experimental method has 
finally been completely launched and set under way. 
Laboratory methods, comparative morphology, embry- 
ological recapitulation, life-history studies, ecological in- 
vestigations — all these means are likely to be overshad- 
owed for a time by experiments in actually growing the 
things under conditions of control. (4) We must study 
great numbers of individuals and employ statistical 
methods of comparison. (5) The doctrine of discontin- 
uous evolution is now clearly before us. (6) We are 
beginning to find a pathway through the bewildering maze 
of hybridization. 



CHAPTER VIII 
HOW DOMESTIC VARIETIES ORIGINATE 

''The key is man's power of accumulative selection: 
nature gives successive variations ; man adds them up 
in certain directions useful to him." This, in Darwin's 
phrase, is the essence of the cultivator's skill in ameliorat- 
ing the vegetable kingdom. So far as man is concerned, 
the origin of the initial variation is largely chance, but 
this start or variation once given, he has the power, in 
most cases, to perpetuate it and to modify its characters. 
There, then, are two very different factors or problems 
in the origination of garden varieties, — the production 
of the first departure or variation, and the subsequent 
breeding of it. Persons who give little thought to the 
subject look upon variation as the end of their endeavors, 
thinking that a form comes into being with all its char- 
acters well marked and fixed. In reality, however, 
variation may be but the beginning in the process ; selec- 
tion is the end so far as the plant-breeder is concerned. 

Indeterminate varieties. — There are two general classes 
of garden varieties in respect to the method of their 
origin, — those that come into existence somewhat 
suddenly and which require little else of the husband- 
man than the multiplication of them, and those that 
p 209 



210 Plant-Breeding 

are the result of a slow evolution or direct breeding. The 
former are indeterminate or uncertain, and the latter are 
determinate or definite. The greater part of those in the 
first class are plants that are multiplied or divided by 
bud-propagation. They comprise nearly all our fruits, 
the woody ornamental plants, and such herbaceous gen- 
era as begonia, canna, gladiolus, lily, dahlia, carnation, 
chrysanthemum, and the like, — in fact, all those multi- 
plied by grafting, cuttings, bulbs, or other asexual parts. 
The original plant may be either a seedling or a bud-sport. 
The gardener, who is always on the look-out for novelties, 
discovers its good qualities and propagates it. 

Varieties which are habitually multiplied by buds, as 
in those plants that have been mentioned in the last para- 
graph, vary widely when grown from seeds, so that every 
seedling may be markedly distinct. As soon, however, as 
varieties are widely and exclusively propagated by seeds, 
they develop a capability of carrying the greater part of 
the individual differences down to the offspring. That 
is, seedlings from bud-multiplied plants do not ''come 
true," as a rule, whilst those from seed-propagated plants 
do ''come true." The reason of this difference will be- 
come apparent on a moment's reflection. In the seed- 
propagated plants, like the kitchen-garden vegetables 
and the annual flowers, we select the seeds and thereby 
eliminate all those variations which would have arisen had 
the discarded seeds been sown. In other words, we are 
constantly fixing the tendency to ''come true," for this 
feature of plants is as much a variation as is form or 
color or any other attribute. Suppose, for example, that a 
certain variation were to receive two opposite treatments, 



How Domestic Varieties Originate 211 

the seeds from one-half of the progeny being carefully 
selected year by year, and all those from untypical plants 
discarded, whilst in the other half all the seeds from all 
the plants, whether good or bad, are saved and sown. In 
the one case, it will be seen, we are fixing the tendency 
to '^come true," for this is all that constitutes a horticul- 
tural variety, — a brood very much like all its parents. 
In the other case, we are constantly eliminating the 
tendency to ''come true" by allowing every modifying 
agency full chance. So the very act of taking seeds only 
from plants that have ''come true," tends still more 
strongly to fix the hereditary force within narrow limits. 
Working against this restrictive force, however, are all 
the agencies of environment and atavism, so that, fortu- 
nately, now and then a seed gives a "rogue," or a plant 
widely unlike its parents, and this may be the start for a 
new variety. 

With bud-multiplied varieties, however, the case is 
very different. Here every seed may be sown, as in the 
illustrative case above, because the seedlings are not 
wanted for themselves, but only as stocks on which 
to bud or graft the desired varieties. So there is no seed 
selection in the ordinary propagation of apples, pears, 
peaches, and the usual orchard fruits. The seeds are 
taken indiscriminately from pomace or the refuse of can- 
ning or evaporating factories. Moreover, many such 
varieties are hybrid, and when propagated by seed, split 
up into many forms. But every annual garden vegetable 
is always grown from seeds more or less carefully saved 
from plants that possess some desired attribute. There is 
no reason why the tree fruits should not reproduce them- 



212 Plant-Breeding 

selves from seeds just as closely as do the annual herbs, 
if they were to be as carefully propagated by selected seeds 
through a long course of generations. There is excellent 
proof of this in the well-marked races or families of Rus- 
sian apples. In that country, grafting had been little 
employed, and consequently it has been necessary to select 
seeds only from acceptable trees in order that the off- 
spring might be more acceptable. So the Russian apples 
have come to run in groups or families, each family bear- 
ing the mark of some strong ancestor. Most of the 
seedlings of the Oldenburg are recognizable because of 
their likeness to the parent. We may thus trace an 
incipient tendency in our own fruits towards racial 
characters. The Fameuse type of apples, for example, 
tends to perpetuate itself ; and a similar tendency is very 
well marked in the Damson and Green Gage plums, the 
Orange quince. Concord grapes, and Hill's Chili and 
Crawford peaches. But inasmuch as bud-multiplication 
is so essential in nursery practice, we can hardly hope 
for the time when our trees and shrubs, or even our per- 
ennial herbs, will ''come true" with much certainty. In 
them, therefore, we get new varieties by simply sowing 
seeds ; but in seed-propagated varieties we must depend 
either on chance variations or else we must resort to 
definite plant-breeding. 

Plant-breeding. — The breeding of domestic animals is 
attended, for the most part, with such definite and often 
precise results that there has come to be a general desire 
to extend the same principles to plants. It is not unusual 
to hear well-informed people say that it is possible to breed 
plants with as much certainty and exactness as it is to 



Holo Domestic Varieties Originate 



213 




73 
O 
O 



2 

'So 

o 

o 

o 



05 






214 



Plant-Breeding 




-a 






c3 

s 

o 

f/3 



> 
o 






CC 



o 
6 



How Domestic Varieties Originate 215 



breed animals. The fact is, however, that such exactness 
will never be possible, because plants are very unlike 
animals in organization, and because, also, the objects 
sought in the two 
cases are character- 
istically unlike. 
Plants, as we have 
seen, are made up 
of a colony of poten- 
tial individuals, and 
to breed between 
two plants by cross- 
ing means that we 
must choose the 
sex-parents from 
amongst as many 
individuals as there 
are flowers or 
branches on the two 
plants, whilst in 
animals we choose 
two definite personal 
parents. And these 

personal parents are Fig. 51. — improving the tomato : A, fruit of 

either male or fe- approximately ideal form secured by cross- 

, 1 , . ing and selection; B, fruit showing im- 

male, and the union perfections and undesirable characters, 

is essential to the (Yearbook, U. S. Dept. Agric.) 

production of offspring, whilst in plants each parent — 
that is, each flower — is usually both male and female 
and the union of two is not essential to the produc- 
tion of offspring, for the plant is capable of multiplying 




216 



Plant-Breeding 



itself by buds. The element of chance, therefore, is one 
hundred, or more, to one in crossing plants as compared 
with crossing animals. Then, again, the plant-parents 
may be modified profoundly by every environmental condi- 
tion of soil and temperature and sunshine, or other ex- 
ternal conditions, since they possess no bodily tempera- 



/s 

/4 
/J 






















///^ 


^ P/ 


:>/: P. 


&■/ 
















/ 






^^ 












/ 






/ 






^^'^> 










/ 


/ 




y 


















/ 


















^ 




\ 
























N 


"\ 


y 


\ 




y 


^l-c 


^yfy 


^t.P 


'9f. 












\ 




y 


^ 




\ 


/ 






















\ 


/ 



^ ^ ^ ^s ^ ^ 



^ 



/L 



*Jf ^O ^Jt ^yy '/■» 



Fig. 52. — Crop averages in corn breeding for high and for low protein. 
Results of twelve generations. (Illinois Experiment Station.) 



ture, no choice of conditions, and no volition to enable 
them to overcome the circumstances in which they are 
placed. Animals, on the contrary, have all these ele- 
ments of personality, and the breeder is also able to con- 
trol the conditions of their lives to a nicety. In view of 
all these facts, it is not strange that animals can be bred 
by crossing with more confidence than can plants. But 
there is another and even more important difference 



HoiD Domestic Varieties Originate 



217 



between the breeding of animals and the breeding of 
plants. In animals, our sole object is to secure simply 
one animal or one brood of offspring. In plants, our 
object is, in general, to secure a race or generation of 




Fig. 53. — Fruit of wild elderberry. 



offspring, which may be disseminated freely over the 
earth. In the bovine race, for example, our object in 
breeding is to produce one cow with given characters; 
in turnips, our object is to produce a new variety, the 
seed of which will reproduce the variety, whether sown in 
Pennsylvania or Ceylon. It is apparent, therefore, that 



218 



Plant-Breeding 



any comparisons drawn between the breeding of animals 
and plants are likely to be fallacious. 

Is there, then, any such thing as plant-breeding, any 
possibility that the operator can proceed with some con- 




FiG. 54. — Fruit of a cultivated variety of the elderberry which appeared 
as a variation from the wild form. 



fidence that he may obtain the ideal he has in mind? 
Yes, to a certain extent. 

Plant-breeding by selection. — It is apparent that the 
very first effort on the part of the plant-breeder must be 
to secure individual differences ; for so long as the plants 



How Domestic Varieties Originate 



219 



that he handles are very closely alike, so long there will 
be little hope of obtaining new varieties. He must, 
therefore, cause his plants to vary. In plants that 
are comparatively unvariable, it is frequently impossible 
to produce variations in the desired direction at once, but 
it is more important to ''break" the type, — that is, to 




Fig. 55. — Field of wilt-resistant watermelons, growing free from disease 
on infected land. (From Yeaibook.) 



make it depart markedly from its normal behavior in 
any or many directions. If the type once begins to vary, 
to break up into different forms, the operator may expect 
that it will soon become plastic enough to allow of modi- 
fication in the ways he desires. But whilst it is impor- 
tant or even necessary to break a well-marked type into 
many forms, it would no doubt be unwise to encourage this 



220 



Plant-Breeding 



tendency after it once appears, lest the plant acquire a too 
strong habit of scattering. This initial variation is induced 
by changing the conditions in which the plant has habit- 
ually grown, as a change of seed, change of soil, tillage, 
varying the food supply, crossing, and the like. 

As a matter of fact, however, nearly all plants that 




Fig. 56. — Disease resistance in cowpeas. Showing a variety which 
is immune (on the left) and a susceptible variety (on the right) 
to cowpea wilt. 

have been long cultivated are already sufficiently variable 
to afford a starting-point for breeding. The operator 
should have a vivid mental picture of the variety which 
he designs to obtain ; then he should select that plant in 
his plantation which is nearest his ideal, and sow the 
seeds of it. From the seedlings he should again select 
his type, and so on, generation after generation, until 



Hotv Domestic Varieties Originate 



221 



the desired object is attained. It is important, if he is 
to make rapid progress, that he keep the same ideal in 





(1) Grand Rapids, one parent 
used in developing improved 
types. 



(2) Golden Queen, the other 
parent used in developing 
improved types. 




(3) New loose type for the 
western market, secured by 
crossing the varieties shown 
in (1) and (2). 




(4) New head type for eastern 
conditions, secured by cross- 
ing the varieties shown in 
(1) and (2). 



Fig. 57. — Improved types of lettuce and the varieties from which 

they were developed. 



mind year after year, otherwise there will be vacillation, 
and the progress of one year may be undone by a counter- 
direction the following year. In this way it will be 



222 Plant' Breeding 

found that almost any character of a plant may be either 
intensified or lessened within certain limits. This is man's 
nearest approach to the Creator in his control over the 
physical forms of fife, and it is great and potent in pro- 
portion as it sets for itself correct ideals in the beginning 
and adheres to them until the end. 

For examples of improvement by selection see Figs. 49- 
56, that represent familiar results. 

RULES FOR BREEDING PLANTS 

When beginning this selection or breeding for an ideal, 
it is important that impossible or contradictory results be 
avoided. Some of the cautions and sugges-tions that 
need to be considered are these : — 

1. Avoid striving after features that are antagonistic 
or foreign to the species or genus with which you are 
working. Every group of plants has become endowed 
with certain characters or lines of development, and the 
cultivator will secure quicker and surer results if he works 
along the same lines, rather than attempt to thwart them. 
Nature gives the hint : let man follow it out, rather than 
to endeavor to create new types of characters. Consider 
some of the solanaceous plants for examples. There 
are certain types of the genus Solanum which have a 
natural habit of tuber-bearing, as the potato. Such 
species should be bred for tubers and not for fruits. There 
are other Solanums, however, as the egg-plants and the 
pepinoes, which naturally vary or develop in the direc- 
tion of fruit-bearing, and these should be bred for fruits 
and not for tubers ; and the same should be true in the 
related genera of tomatoes, red peppers, and physalis. 



How Domestic Varieties Originate 223 

Those ambitious persons who are always looking for a 
tuber-bearing tomato, therefore, might better concen- 
trate their energies on the potato, for the tomato is not 
developing in that direction ; and even if the tomato 
could be made to produce tubers, it would thereby lessen 
its fruit production, for plants cannot maintain two diverse 
and profitable crops at the same time. It is more rea- 
sonable, and certainly more practicable, to grow potatoes 
on potato plants and tomatoes on tomato plants. 

2. The quickest and most marked results are to be ex- 
pected in those groups or species which are normally the 
most variable. There are a greater number of variations 
or starting-points in such species ; but it also follows that 
the forms are less stable, the more the species is variable. 
Yet the variations, being very plastic, yield themselves 
readily to the wishes of the operator. Carri^re puts the 
thought in this form: ''The stabihty of forms, in any 
group of plants, is, in general, in inverse ratio to the num- 
ber of the species which it contains, and also to the degree 
of its domestication." 

The most variable types are the most dominant ones 
over the earth ; that is, they occur in greater numbers 
and under more diverse conditions than the compara- 
tively invariable types do. The Compositse, or sunflower- 
hke plants, comprise a ninth or tenth of the total species 
of flowering plants, and the larger part of the subordinate 
types or genera contain many forms or species. Aster, 
goldenrod, the hawkweeds, thistles, and other groups, are 
representative of the cosmopolitan or variable types of 
composites. Whenever, for any reason, any type begins to 
decline in variabiHty, it usually begins to perish ; it is then 



224 Plant-Breeding 

tending towards extinction. Monotypic genera — those 
which contain but a single species — are usually of local 
or disconnected distribution, and are probably, for the 
most part, vanishing remnants of a once important type. 
As a rule, most of our widely variable and staple culti- 
vated species are members of large, or at least polytypic, 
genera. Such, for example, are the apples and pears, 
peaches and plums, oranges and lemons, roses, bananas, 
chrysanthemums, pinks, cucurbits, beans, potatoes, 
grapes, barley, rice, cotton. A marked exception to this 
statement is maize, which is immensely variable and is 
generally held to have come from a single species ; but 
the genesis of maize is unknown, and it is possible that 
more than one species is concerned in it. Wheat is also 
a partial exception, although the original specific type is 
not understood ; and the latest monographers admit three 
or four other species to the genus, aside from wheat. 
There are other exceptions, but they are mostly unim- 
portant, and, in the main, it may be said that the domi- 
nant domestic types of plants represent markedly poly- 
typic genera. 

3. Breed for one thing at a time. The person who 
strives at the same time for increase or modification in 
proUficacy and flavor will be likely to fail in both. He 
should work for one object alone, simply giving sufficient 
attention to subsidiary objects to keep them up to normal 
standard. This is really equivalent to saying that there 
can be no such thing as the perfect all-around variety that 
so many people covet. Varieties must be adapted to 
specific uses, — one for shipping, one for canning, one for 
dessert, one for keeping qualities, and the like. The 



How Domestic Varieties Originate 225 

more good varieties there are of any species, the more 
widely and successfully that species can be cultivated. 
A knowledge of Mendel's laws of heredity assists the 
breeder to secure more rapidly the proper combination 
of qualities and to fix them. 

4. Do not desire contradictory attributes in any variety. 
A variety, for example, that bears the maximum number 
of fruits or flowers cannot be expected greatly to increase 
the size of those organs without loss in numbers. This is 
well shown in the tomato. The original tomato produced 
from six to ten fruits in a cluster, but as the fruits in- 
creased in size the numbers in each cluster fell to two or 
three. That is, increase in size proceeded somewhat at 
the expense of numerical productivity ; yet the total 
weight of fruit to the plant has greatly increased. The 
same is true of apples and pears ; for whilst these trees bear 
flowers in clusters, they generally bear their fruits singly. 
Originally, every flower normally set fruit. The reason 
why blackberries, currants, and grapes do not increase 
more markedly in size, is probably because the size of 
cluster has been given greater attention than the size of 
berry. Plants which now bear a full crop of tubers can- 
not be expected to increase greatly in fruit bearing, as 
already explained under Rule 1. This fact is illustrated 
in the potato, in which, as tuber-production has increased, 
seed-production has decreased, so that growers now com- 
plain that potatoes do not produce bolls as freely as they 
did years ago. 

5. When selecting seeds, remember that the character 
of the whole plant is more important than the character 
of any one branch or part of the plant ; and the more 

Q 



226 Plant-Breeding 

uniform the plant in all its parts, the greater is the likeli- 
hood that it will transmit its characters. If one is striv- 
ing for larger flowers, for example, he \Adll secure better 
results if he choose seeds from plants that bear large 
flowers throughout, than he will if he choose them from 
some one of the large flowering branches on a plant that 
bears indifferent flowers on the remaining branches, even 
though this given branch produces much larger flowers 
than those borne on the large-flowered plant. Small 
potatoes from productive hills give a better product than 
large potatoes from unproductive hills. The habit of 
selecting large ears from a bin of corn, or large melons 
from the grocer's wagon, is much less efficient in producing 
large products the following season than the practice of 
going into the fields and selecting the most uniformly 
large-fruited parents. A very poor plant may occasion- 
ally produce one or two very superior fruits, but the seeds 
are more Hkely to perpetuate the characters of the plant 
than of the fruits. 

The following experiences detailed by Henri L. de 
Vilmorin illustrate the proposition admirably: ''I tried 
an experiment with seeds of Chrysanthemum carinatum 
gathered on double, single, and semi-double heads, all 
growing on one plant, and found no difference whatever 
in the proportion of single and double-flowered plants. 
In striped verbenas, an unequal distribution of the color 
is often noticed ; some heads are pure white, some of a 
self-color, and most are marked with colored stripes on 
white ground. I had seeds taken severally from all and 
tested alongside one another. The result was the same. 
All the seeds from one plant, whatever the color of the 



How Domestic Varieties Originate 227 

flower that bore them, gave the same proportion of plain 
and variegated flowers." 

The second part of the proposition is equally as impor- 
tant as the first, — the fact that a plant which is uniform 
in all its branches or parts is more Ukely to transmit its 
general features than one which varies within itself. 
It is well known that bean plants often produce beans 
with various styles of markings on the same plant or even 
in the same pod, yet these variations rarely, if ever, perpet- 
uate themselves. The same remark may be apphed to 
variations in peas. These illustrations only add emphasis 
to the fact that intending plant-breeders should give 
greater heed than they usually do to the entire plant, 
rather than confine their attention to the particular 
part or organ which they desire to improve. 

At first thought, it may look as if these facts are 
directly opposed to the proposition emphasized in the first 
chapter that every branch of a plant is a potential auton- 
omy, but it is really a confirmation of it. The variation 
itself shows that the branch is measurably independent, 
but it is not until the conditions or causes of the variation 
are powerful enough to affect the entire plant that they 
are sufficiently impressed upon the organization of the 
plant to make their effects hereditary through seeds. 

There is an apparent exception to the law that the 
character of the entire plant is more important than any 
one organ or part of it, in the case of the seeds themselves. 
That is, better results usually follow the sowing of large 
and heavy seeds than of small or unselected seeds from the 
same plant. This, however, does not affect the main 
proposition, for the seed is in a measure independent of 



228 Plant-Breeding 

the plant body, and is not so directly influenced by envi- 
ronment as are the other organs. And, again, the seed 
receives a part of its elements from a second or male 
parent. The good results which follow the use of large 
seeds are, chiefly, greater uniformity of crop, increased 
vigor, often a gain in earliness and sometimes in bulk, 
and usually a greater capacity for the production of 
seeds. These results are probably associated less with 
any innate hereditable tendencies than with the mere 
vegetative strength and uniformness of the large seeds. 
The large seeds usually germinate more quickly than the 
small ones, provided both are equally mature, and they 
push the plantlet on more vigorously. This initial 
gain, coming at the most critical time in the life of the new 
individual, is no doubt responsible for very much of the 
result that follows. The uniformity of crop is the most 
important advantage which comes of the use of large 
seeds, and this is obviously the result of the elimination of 
all seeds of varying degrees of maturity, of incomplete 
growth and formation, and of low vitaUty. 

Another important consideration touching the selection 
of seeds, is the fact that very immature seeds give a feeble 
but precocious progeny. This has long been observed 
by gardeners, but Sturtevant, Arthur, and Goff have made 
a critical examination of the subject. ''It is not the 
sHghtly unripe seeds that give a noticeable increase in 
earUness," according to Arthur, ''but very unripe seeds, 
gathered from fruit (tomatoes) scarcely of full size and 
still very green. Such seeds do not weigh more than 
two-thirds as much as those fully ripe. They germinate 
readily and are more easily affected by retarding or harm- 



How Domestic Varieties Originate 229 

ful influences. If they can be brought through the early 
period of growth and become well estabhshed, and the 
fohage or fruit is not attacked by rots or blights, the 
grower will usually be rewarded by an earlier and more 
abundant crop of sHghtly smaller and less firm fruit. 
These characters will be more shghtly emphasized in sub- 
sequent years by continuous seed propagation." Goff 
remarks that the increase in earliness in tomatoes, fol- 
lowing the use of markedly immature seeds, ''is accom- 
panied by a marked decrease in the vigor of the plant, and 
in the size, firmness, and keeping quality of the fruit." 
These results are probably closely associated with the 
chemical constitution and content of the immature seeds. 
The organic compounds have probably not yet reached 
a state of stabiUty, and therefore they respond quickly 
to external stimuli when placed in conditions suitable to 
germination ; and there is httle food for nourishment of 
the plantlet. The consequent weakness of the plantlet 
results in a loss of vegetative vigor, which is earliness. 
(See Rule 2.) 

Still another feature connected with the choice of seeds 
is the fact that in some plants, as in various Ipomoeas, for 
example, the color of the seed is more or less intimately 
associated with the color of the flower which produced 
them and also with the color of the flower which they 
will produce. 

6. Plants that have any desired characteristics in 
common may differ widely in their abiUty to transmit 
these characters. It is usually impossible for the cul- 
tivator to determine, from the appearance of any given 
progeny, which is the most unvariable and the most Uke 



230 Plant- Breeding 

its parent ; but it may be said that those individuals that 
grow in the most usual or normal environments are most 
likely to perpetuate themselves. A very unusual condi- 
tion, as of soil, moisture, or exposure, is not easily im- 
itated when providing for the succeeding generation, and 
a return to normal conditions of environment may be ex- 
pected to be followed by a more or less complete return 
to normal attributes on the part of the plant. If the same 
variation, therefore, were to occur in plants growing under 
widely different conditions, the operator who wishes to 
preserve the new form should take particular care to 
select his seeds from those individuals that seem to have 
been least influenced by the immediate conditions in 
which they have grown. 

Again, if the same variation appears both in uncrossed 
and crossed plants, the best results should be expected 
in selecting seeds from the former. We have already 
seen, in the seventh chapter, how it is that crosses are 
unstable, and how the unstability is likely to be the 
greater the more violent the cross. ''Cross-breeding 
greatly increases the chance of wide variation," writes 
Henri L. de Vilmorin, ''but it makes the task of fixation 
more difficult." 

It is very important, therefore, when selecting seeds 
from plants which seem to give promise of a new variety, 
to sow seeds of each plant separately, and then make the 
subsequent selections from the most stable generation ; 
and it is equally important that the operator should not 
trust to a single plant as a starting-point, whenever he 
has several promising plants from which to choose. 

7. The less marked the departure from the genus of 



How Domestic Varieties Originate 231 

the normal type, the greater, in general, is the likeli- 
hood that it will be perpetuated, although this may 
not be true of sports. This is admirably illustrated in 
crosses. The seed-progeny of crosses between closely 
related varieties, or between different plants of the same 
variety, is more uniform and usually more easy of improve- 
ment by selection than the progeny of hybrids. In un- 
crossed plants, the general tendency is to resemble their 
parents, and the greater the number of like ancestors, 
the greater is the tendency to ^'come true." There is 
thought to be a tendency, though necessarily a weak 
one, to return to some particular ancestor, or to ''date 
back." This is known as atavism. The so-called ata- 
vistic forms are likely to be unstable, to break up into 
numerous forms, or to return more or less completely to 
the type of the main line of the ancestry. The following 
statements touching some of the relations of atavism to 
the amelioration of plants are the results of an excellent 
study of heredity in lupines by Louis Leveque-de Vil- 
morin : — 

''1. The tendency to resemble its parents is generally 
the strongest tendency in any plant ; 

''2. But it is notably impaired as it comes into conflict 
with the tendency to resemble the general line of its 
ancestry. 

''3. This latter tendency, or atavism, is constant, 
though not strong, and scarcely becomes impaired by the 
intervention of a series of generations in which no rever- 
sion has taken place. 

''4. The tendency to resemble a near progenitor (only 
two or three generations removed), on the other hand, is 



232 Plant-Breeding 

very soon obliterated if the given progenitor is different 
from the bulk of its ancestors." 

8. The crossing of plants should be looked upon as a 
means or starting-point, not as an end. We cross two 
flowers and sow the seeds. The resulting seedlings may 
be unlike either parent (see Fig. 57). Here, then, is varia- 
tion. The operator should choose that plant which most 
nearly satisfies his ideal, and then, by selection from its 
progeny and the progeny of succeeding generations, gradu- 
ally obtain the plant which he desires. It is only in plants 
which are propagated by asexual parts — as grafts, cut- 
tings, layers, bulbs, and the like — that hybrids or crosses 
are commonly immediately valuable ; for in these plants 
we really cut up and multiply the one individual plant 
which pleases us in the first batch of seedlings, rather than 
to take the offspring or seedlings of it. Thus, if any par- 
ticular plant in a lot of seedlings of crosses of cannas, or 
plums, or hops, or strawberries, or potatoes, is valuable, 
we multiply that one individual. There is no reason for 
fixing the variety. But any satisfactory plant in a lot of 
seedlings of crosses of pumpkins, or wheat, .or beans, must 
be made the parent of a new variety by sowing the seeds 
of it and then by selecting for seed-parents, year by year, 
those plants which are the best. ^'The unsettled forms 
arising from crosses," Focke writes, ''are the plastic 
material out of which gardeners form their varieties." 

But even in the fruits, and other bud-propagated 
plants, crossing may often be used to as good advantage 
for the purpose of originating variation as it may in peas 
or buckwheat. It only requires a longer time to fix and 
select variations because the plants mature so slowly. 



How Domestic Varieties Originate 233 

Ordinarily, if the operator does not find satisfactory plants 
among the seedlings of any cross of fruit trees, he roots 
up the whole batch as profitless. But if he were to allow 
the best plants to stand and were to sow seeds from them, 
the second generation might produce something more to 
his liking. But it is generally quicker to make another 
cross and to try the experiment over again, than to wait 
for unpromising seedlings to bear. This repeated repeti- 
tion of the experiment, however, — continual crossing 
and sowing and uprooting, — is gambling. Throwing dice 
to see what will turn up is a comparable proceeding. 
The sowing of uncrossed seed is little better. Peter M. 
Gideon sowed over a bushel of apple seed, and one seed 
produced the Wealthy apple.^ D. B. Wier raised a mil- 
lion seedlings of soft maple, and one plant of the lot had 
finely divided leaves, and is now Wier's Cut-leaved maple. 
Teas' Weeping mulberry, which is now so deservedly 
popular, was, as Mr. Teas tells me, ''merely an accidental 
seedhng." So this explains why the production of new 
varieties of fruits is always chance, while a skilled man 
can sit in his study in the winter time and picture to 
himself a new bean or muskmelon, and then go out in the 
next three or four summers and produce it. 

9. If it is desired to employ crossing as a direct means 

1 The facts in the origination of the Wealthy apple, as related to me 
by Mr. Gideon, are these : he first planted a bushel of apple seeds and 
then each year, for nine years, he planted enough to give a thousand trees. 
At the end of ten years, all the seedlings had perished (this was in Min- 
nesota) except one hard seedling crab. Then a small lot of seeds of 
apples and crab apples was obtained in Maine, and from these the 
Wealthy came. There were only about fifty seeds in the batch of crab 
seed which gave the Wealthy; but before this variety was obtained, 
much over a bushel of seed had been sown. 



234 Plant-Breeding 

of producing new varieties, each parent to the proposed 
cross should be chosen in agreement with the rules already 
specified, and also because it possesses in an emphatic 
degree one or more of the qualities which it is desired to 
combine ; and the more uniformly and persistently the 
parent presents a given character, the greater is the chance 
that it will transmit that character. It has already been 
said that crossing for the instant production of new va- 
rieties is most certain to give valuable results in those 
species which are propagated by buds, because the initial 
individual differences are not dissipated by seed reproduc- 
tion. This is especially true of crossing between distinct 
species ; for in such violent crossing as this the offspring 
is particularly likely to be unstable when propagated by 
seeds. The results of hybridization appear to be most 
certain in those plants grown under glass, and in which, 
therefore, the selection of the seed-parents is most care- 
fully made, and where the conditions of existence are 
most uniform. The most remarkable results in hybridiza- 
tion yet attained are with the choicer glass-house plants, 
such as orchids, begonias, anthuriums, and the like. 

The more violent the cross, the less is the likelihood 
that desirable offspring will follow. Species which refuse 
to give satisfactory results when hybridized directly or 
between the pure stocks, may give good varieties when 
the "blood" has become somewhat attenuated through 
previous crossings. The best results in hybrichzing our 
native grape with the European grape, for example, have 
come from the use of one parent which is already a hy- 
brid. Two notable examples are the Brighton and Diamond 
Grapes, raised by Jacob Moore. The Brighton is a cross 



How Domestic Varieties Originate 235 

of Concord (pure native) by Diana-Hamburg (hybrid of 
impure native and European). Diamond is a cross of 
Concord by lona, the latter parent undoubtedly of impure 
origin, containing a trace of the European vine. T. V. 
Munson's Brilliant is a secondary hybrid, its parents, 
Lindley and Delaware, both containing hybrid blood. 
Others of his varieties have similar histories. Even when 
the cross is much attenuated — or three or four or even 
more times removed from a pure hybrid origin by means 
of subsequent crossings — it may still produce marked 
effects in a cross without introducing such contradictory 
characters as to jeopardize the value of the offspring. 

Among American fruit plants there are comparatively 
few valuable species-hybrids. The most conspicuous are 
grapes, particularly the various Rogers varieties, such 
as Agawam, Lindley, Wilder, Barry, and others, which 
are hybrids of the European and native species. Other 
hybrids are the Keiffer and allied pears (between the 
common pear and the Oriental pear), probably the 
Transcendent and a few other crabs (between the com- 
mon apple and the Siberian crab), the Soulard and kin- 
dred crabs (between the common apple and the native 
Western crab), a few blackberries of the Wilson Early 
type (between the blackberry and the dewberry), the 
purple-cane raspberries (between the native red and 
black raspberries, and possibly sometimes combined with 
the European raspberry), the Utah Hybrid cherry (be- 
tween the Western sand cherry and the sand plum), prob- 
ably some plums, and a few others. There is undoubtedly 
a fertile field for further work in hybridizing our fruits, 
particularly those of native origin, and also many of the 



236 '■ Plant-Breeding 

ornamental plants ; the danger is that persons are likely 
to expect too much from hybridization, and too little 
from the betterment of all the other conditions which so 
profoundly modif}^ plants. Violent hybridizations gen- 
erally give unsatisfactory and unreliable results; but 
subsequent crossings, when the ''blood" of the original 
species to the contract is considerably attenuated, may be 
expected to correct or overcome the first incompatibility, 
as explained above. 

10. Establish the ideal of the desired variety firml}^ in 
mind before any attempt is made at plant-breeding. If 
one is to make any progress in securing new varieties, he 
must first be an expert judge of the capabilities and merits 
of the plants with which he is dealing, otherwise he may 
attempt the impossible or he may obtain a variety that 
has no merit. Make frequent use of a score-card to famil- 
iarize yourself with all details. It is important, also, 
that the person bear in mind the fact that a variety which 
is simply as good as any other in cultivation is not worth 
introducing. It should be better in some particular than 
any other in existence. The operator must know the 
points of his plant, as an expert stock-breeder knows the 
points of an animal, and he must possess the rare judgment 
to determine which characters are most likely to reappear 
in the offspring. Inasmuch as a person can be an expert 
in only a few plants, it follows that he cannot expect satis- 
factory results in breeding any species that may chance 
to come before him. Persistent and uniform effort, con- 
tinued over a series of years, is usually demanded for 
the production of really valuable varieties. Thus it often 
happens that one man excels all competitors in breeding a 



How Domestic Varieties Originate 237 

particular class of plants. The horticulturists will recall, 
for example, Lemoine in the breeding of gladiolus, Eckford 
in peas, Crozy in cannas, Bruant in pelargoniums, and 
others. There are now and then varieties which arise 
from no effort, but because of that very fact they reflect 
no credit upon the so-called originator, who is really only 
the lucky finder. So far as the originator is concerned, 
such varieties are merely chance. If, however, the 
operator — himself an expert judge of the plant with 
which he deals — chooses his seeds with care and dis- 
crimination, and then proposes, if need be, to follow up 
his work generation after generation of plants by means 
of selection, the work becomes plant-breeding of the 
highest type. 

First of all, therefore, the operator must know what 
he can likely get, and what will likely be worth getting. 
Many persons, however, begin at the other end of the 
problem, — they get what they can, and then let 
the public judge whether the effort has been worth 
the while. 

11. Having derived a specific and correct ideal, the 
operator must next seek to make his plant vary in the 
desired direction. This may be done by crossing, or by 
modifjdng the conditions under which the plant grows. 
If there are any two plants that possess indications of 
the desired attributes, cross them ; among the seedhngs 
there may be some that may serve as starting-points for 
further effort. 

A change in the circumstances or environment of the 
plant may start the desired attribute. If the plant must 
be dwarfer, plant it on poorer or drier soil, transfer it 



238 Plant-Breeding 

towards the poles, plant it late in the season, or transplant 
it repeatedly. Dwarf peas become climbing peas on rich, 
moist lands. If the plant must have large fruits, allow it 
more food and room, and give attention to pruning and 
thinning. Certain geographical regions develop certain 
characters in plants, as we have seen; if, therefore, the 
desired feature does not appear spontaneously or as a 
result of any other treatment, transfer the plant for a 
time to that region which is characterized by such attri- 
butes, if there is any such. It is not intended to convey 
the impression that the placing of plants on poor soil will 
directly cause a dwarfing which will be inherited, or large 
size on good soils, but if the plant already holds the 
characteristic of dwarfness or some other quahty in a 
latent form, it will probably appear if the conditions are 
made right. 

The importance of growing the plant under conditions 
or environments in which the desired type of characters 
is most frequently found, is admirably emphasized in the 
evolution of varieties which are adapted to forcing under 
glass. Within a century — and in many instances within 
a score of years — species that are practically unknown 
to glass-houses have produced varieties perfectly adapted 
to them. This has been accomplished by growing the 
most tractable existing varieties, selecting those which 
most completely adapt themselves to their environment 
and to the ideals of the operator. One of the most re- 
markable examples of this kind is afforded by the carna- 
tion. In Europe it was chiefly a border or outdoor plant, 
but within a generation it had produced hosts of excellent 
forcing varieties in America, where it is grown almost ex- 



Hoiv Domestic Varieties Originate 239 

clusively as a glass-house flower. So the carnation types 
of Europe and America have been widely unlike. 

Sowing the seeds of hardy annual plants in autumn 
often stimulates a tendency to produce thickened roots. 
The plant, finding itself unable to perfect seeds, stores its 
reserve in the root, and it therefore tends to become 
biennial. In this manner, with the aid of selection and 
the variation of the soil, Carriere was able to produce 
good radishes from the wild slender-rooted charlock 
(Raphanus Raphanistrum) . 

Lessened vigor, so long as the plant continues to be 
healthy, nearly always results in a comparative increase of 
fruits or reproductive organs. It is an old horticultural 
maxim that checking growth induces fruitfulness. It is 
largely in consequence of this fact that plants bear heaviest 
when they attain approximate maturity. Trees are 
often thrown into bearing by girdling, heavy pruning, 
the attacks of borers, and various accidental injuries. 
The gardener knows that if he keeps his plants in vigorous 
growth by constantly putting them into larger pots, he 
will get Httle, or at least very late, bloom. The plant- 
breeder, therefore, may be able to induce the desired 
initial variation by attention to this principle. (See dis- 
cussion of variation in relation to food supply.) Arthur 
has recently put the principle into this formula: '^A 
decrease in nutrition during the period of growth of an 
organism favors the development of the reproductive 
parts at the expense of the vegetative parts." 

A most important means of inducing variation is the 
simple change of seed, the philosophical reasons for 
which are explained on earher pages. A plant becomes 



240 



Plant-Breeding 



closely fitted or accustomed to one set of conditions, and 
when it is placed in new conditions, it at once makes an 
effort to adapt itself to them. This adaptation is varia- 
tion. No doubt the free interchange of seeds between 
seed-merchants and customers is one of the causes of 
the enormous increase in varieties in recent times. 

When once a novel variety appears, others of a similar 
kind are likely soon to follow in other places, and some 

persons have supposed 
that there is a synchro- 
nistic variation in 
plants, or a tendency 
for like variations to 
appear simultaneously 
in widely separated lo- 
calities. There is per- 
haps some remote reason 
for this opinion, because 
there is, as Darwin ex- 
presses it, an accumula- 
tive effect of domestica- 
tion or cultivation, by virtue of which plants that long 
remain comparatively invariable may, within a short 
time, when cultivation has been continued long enough, 
vary widely and in many directions ; and it is to be ex- 
pected that even when plants have long since responded 
to the wishes of the cultivator, an equal amount or accumu- 
lation of the force of domestication would tend to produce 
like effects in different places. But it is probable that by 
far the greater part of this synchronistic variation is 
simply apparent, for whenever any marked novelty appears 




Fig. 58. — Wild cabbage. 



Hoic Domestic Varieties Originate 



241 



the attention of all interested persons is directed to looking 
for similar variations amongst their own plants. 

12. The person who is wishing for new varieties should 
look critically to all perennial plants, and particularly to 
trees and shrubs, for bud-varieties or sports. It has 
already been said that the branches of a tree may vary 
among themselves in the same way in which seedhngs 




Fig. 59. — Curled kale. Brassica oleracea var. acephala. 



vary, and for the same reason. As a rule, any marked 
sport is capable of being perpetuated by bud-propagation. 
The number of bud-varieties now in cultivation is really 
very large. Many of the cut-leaved and colored or 
variegated varieties of ornamental plants were originally 
found on other trees as sports. The ''mixing in the 
hill" of potatoes is bud-variation. Nectarines are de- 
rived from the peach, some of them as sports and some as 
seedhngs. The moss-rose was probably originally a sport 

R 



242 



Plant- Breeding 



from the Provence rose. Greening apple trees often bear 
Russet apples, and Russets sometimes bear Greenings. 

Bud-varieties may not only come from buds, — as 
grafts, cuttings, and layers, — but they sometimes 
perpetuate themselves by seeds. Now, these seedlings 

are amenable to selec- 
tion, just the same as 
any other seedlings are ; 
the bud-variety, there- 
fore, may give the in- 
itial starting-point for 
plant-breeding. But, 
more than this, it is 
sometimes possible to 
improve and fix the 
type by bud-selection 
as well as by seed-se- 
lection. Darwin cites 
this interesting testi- 
mony : ''Mr. Salter 
brings the principle of 
selection to bear on 
variegated plants prop- 
agated by buds, and has thus greatly improved and 
fixed several varieties. He informs me that at first a 
branch often produces variegated leaves on one side alone, 
and that the leaves are marked only with an irregular 
edging, or with a few lines of white and yellow. To im- 
prove and fix such varieties, he finds it necessary to en- 
courage the buds at the bases of the most distinctly marked 
leaves and to p""opagate from them alone. By following, 




Fig. 60. — Collard. 



How Domestic Varieties Originate 



243 



with perseverance, this plan during three or four successive 
seasons a distinct and fixed variety can generally be 
secured." Ernest Walker, then a gardener at New Al- 
bany, Indiana, is of the opinion that the abnormal charac- 
ter of sports often intensifies itself if the sport is allowed 
to remain on the parent plant for a considerable time. 
He has observed this particularly in coleus, where color 
sports are frequent. ''In these," he says, ''the sport 
begins with a branch which may 
be taken off and propagated as 
a new variety. If left on the 
parent, other parts of the plant 
are apt to show similar varia- 
tions. Indeed, I think it is not 
best to be in too great hurry to 
remove a sporting branch, for its 
character seems to tend to be- 
come more fixed if it remains on 
the plant." 

13. The starting-point once 
given, all permanent progress lies 
in continued selection. This, as 
we have already pointed out, is really the key to the whole 
matter. In the great number of cases, the operator cannot 
produce the initial variation which he desires, but, by look- 
ing carefully among many plants, he may find one which 
shows an indication of his ideal. This plant must be 
carefully saved, and all of the seeds sown in a place where 
crossing with other types cannot take place. Of a hundrtHl 
seedUngs from this plant, perhaps one or two will still 
further emphasize the character which is sought. These, 




Fig. 61. — Brussels sprouts. 



244 



Plant- Breeding 



again, are saved, and all the seeds are sown. So the 
operation goes on, patiently and persistently, and there is 
a reward at the end. This is the one fundamental practice 
that underlies the amelioration of plants under the touch 
of man ; and because we know, from experience, that it 
is so important, we are sure, as Darwin was, that selec- 
tion in nature must be a factor in the progress of the 
vegetable world. 

But suppose this suggestion of the new variety does 

not appear among the 
batch of plants that 
we raise ? Then sow 
again ; vary the con- 
ditions; choose the 
most widely variable 
types ; cross ; at length 

— if the ideal is true 

— the suggestion will 
come. ''Cultivation, 
diversification of the 
conditions of existence^ 

and repeated sowings" are the means which Verlot 
would employ to induce variations. But the skill and 
the character of the final result he not so much in the 
securing of the initial start, as in the subsequent se- 
lection. Nature affords starting-points in endless num- 
bers, but there are few men alert and skillful enough 
to take the hint and improve it. If we want a new 
tomato, we first endeavor to discover what we want. We 
decide that we must have one hke the Acme in color, but 
more spherical, with a firmer flesh, and a httle earlier. 




Fig. 62. — Savoy cabbage. 



How Domestic Varieties Originate 



245 



Then we shall raise an acre of Acme tomatoes, and closel}^ 
allied varieties ; if we cannot do that, we make arrange- 
ments to inspect the neighbor's fields. We scrutinize 
every plant as the first fruits are ripening. Finally, one 
plant is found — not one fruit — which is something like 
the variety desired. Very well. Wait two to five j^ears 
and you shall see the new variety. 










Fig. 63. — Cabbage shapes: flat; round or ball; egg-shaped; oval; 

conical. 

Some of these initial variations possess no tendency to 
reproduce themselves. The seedUngs of them may break 
up into a great diversity of forms, no form representing 
the parent closely. In such cases, it is generally useless 
to proceed further with this brood. Another start 
should be made with another plant. So it is alwaj^s im- 
portant, as we have already seen (Rule 6), to have as 



246 Plant-Breeding 

many starting-points as possible, to lessen the risk of 
failure. Whilst it requires nice judgment to choose 
those plants which possess the most important and the 
most transmissible combination of characters, the great- 
est skill is nevertheless required to carry forward a correct 
system of selection. 

14. Even when the desired variety is obtained, it must 
be kept up to the standard by constant attention to 
selection. That is, there is no real stability in the forms 
of Ufe. So long as the conditions of existence vary, 
so long will the plants make the effort to adapt themselves 
to the changes. No two seasons are alike ; and no two 
fields, or even parts of fields, are alike ; and there are no 
two cultivators who give exactly the same and equal at- 
tention to tillage, fertilizing, and the other treatment of 
plants. All forms or varieties, therefore, tend to ''run 
out" by variation or gradual evolution into other forms; 
but because we keep the same name for all the succeeding 
generations, we fancy that we still have the same variety. 

" In 1887 I found a single tomato plant in my garden 
in Michigan, that had several points of superiority over 
any other of the one hundred and seventy varieties I 
was then growing. It came from a packet of German 
seed of an inferior variety. The tomato was very solid, 
an unusually long keeper, productive, and attractive in 
size and appearance. The variation was so promising 
that I named it in a sketch of tomatoes that I pubHshed 
that year, calhng it the Ignotum (that is, unknown), 
to indicate that the origin of it was no merit of my own. I 
sent seeds to a few friends for testing. I sowed the seeds 
for about five hundred plants in 1888 in an isolated patch 



How Domestic Varieties Originate 247 

on uniform soil. The larger part of the plants were more 
or less like the parent. A few reverted. A few of the 
best plants were selected and the seed saved. I then 
moved to New York and took the seed with me. This 
was sown in uniform soil in an isolated position in 1889. 
This crop, probably as a result of the careful selection of 
the year before and of the change of locality, was re- 
markably uniform and handsome. Of the 442 plants 
I grew that year, none reverted to the little Eiformige 
Dauer, the German variety from which it had come, but 
there was some variation in them due to different methods 
of treatment. I again saved the seeds, and I was now 
ready to introduce the variety. I therefore sold my seeds, 
six pounds, to V. H. Hallock & Son, Queens, New York, 
who introduced it in 1890. The very next year, 1891, I 
obtained the Ignotum from fifteen dealers and grew the 
plants side by side. Of the fifteen lots, eight bore small 
and poor fruits which were not worth growing and which 
could not be recognized as Ignotum ! Grown from our 
own seeds, it still held its character well. Here, then, 
only a year after its introduction, half the seedsmen were 
selling a spurious stock. It is possible that some of this 
variation arose from substitution of other varieties by 
seedsmen, although I have yet secured no evidence of any 
unfair deahng. It is possible, also, that the product of 
some of the samples which I early sent out for testing had 
found their way into seedsmen's hands. But I am 
convinced that very much of this variation was a legiti- 
mate result of the various conditions in which the crops of 
1890 had been grown, and the varying ideals of those who 
saved seeds. I am the more positive of this from the 



248 



Plant-Breeding 




fact that the Ignotum tomato, as I first knew it and bred 
it, appears now to be lost to cultivation, although the name 

is still used for the legitimate 
family of descendants from my 
original stock. All this experi- 
ence illustrates how quickly varie- 
ties pass out by variation and by 
the unconscious and unlike selec- 
tion practiced by different per- 
sons." — ^ Bailey, earher editions. 

The longevity of any variety 
is inversely proportional to the 
frequency of its generations. An- 
nual plants, other conditions 
being the same, run out sooner 
than perennials, because seed-re- 
production — or the generations 
— intervenes more frequently. 
Trees, on the other hand, carry 
their variations longer, because 
the seed generations — in which 
departures chiefly take place — 
are farther apart. Of all the so- 
called fruit plants, the strawberry 
runs out soonest and the varie- 
ties change the oftenest, because 
a new generation can be brought 
into fruit-bearing in two years, 
whilst it may require ten years or 
more to bring a new generation of apples or chestnuts into 
bearing. '^ Yet, my reader will remind me that the Wilson 




Fig. 64. — Swede turnip 
(top) ; kohl-rabi (middle) ; 
cauliflower (bottom). 



How Domestic Varieties Originate 249 

strawberry has been and is the leading variety in many 
places for nearly forty years, to which I reply that the Wilson 
of to-day is not necessarily the same as that introduced 








Fig. 65. — Wild form of Chrysanthemum morifolium,, as grown in 

England. 

by James Wilson, simply because the name is the same. 
Every different soil or treatment tends to produce a different 
strain or variation in the Wilson strawberr}^, as it does in 
any other plant ; anti every grower, when setting a new 



250 



Plant-Breeding 



plantation, chooses his plants from that part of his field 
which pleases him best, rather than from those plants 
that most nearly correspond to the original type of the 
Wilson. That is, the unconscious selection on the part 
of the grower takes no account of what the variety was, 
but only of what it ought to be, and this ideal differs with 




Fig. 66. — Wild form of Chrysanthemum indicum, as grown in England. 



every person. It is not surprising, therefore, to find strains 
of Wilson strawberry as unlike as are many named vari- 
eties ; and it is to be expected that all the strains now in 
existence have departed considerably from the original 
type." — Bailey, earlier editions. 

This example borrowed from the strawberry is a most 
important one, because it illustrates how a variety may 



How Domestic Varieties Originate 251 



. ^' ff /'. 



vary and pass out of existence even though it is propa- 
gated wholly asexually or by buds. There are to-day 
several different types of Rhode Island Greening apple in 
cultivation which have probably originated from varia- 
tions induced by environment and by the different ideals 
of propagators ; and the same is true in other fruits. 

All the foregoing remarks illustrate the importance 
of constant attention to selection if 
one desires to maintain the exact 
type of any variet}^ which he has 
produced. They explain the value 
of the "roguing" — or systematic 
destruction of all ''rogues" or non- 
typical plants — which is invariably 
practiced by all good seed growers. 
But they still more emphatically 
show that every variety is essen- 
tially unstable, and that the only 
abiding result is constant evolution, 
the old forms being left behind as 
the type expands into new and 
better forms. Varieties to be valu- 
able, therefore, ought not to be rigidly fixed, and, for- 
tunately, nature has prescribed that they cannot be. 
Probably every ten years sees a marked change in every 
variety of any annual species which is propagated ex- 
clusively from seeds, and every century must see a like 
change in the tree fruits. These changes are so gradual 
and the original basis of comparison fades away so com- 
pletely that we generally fail to recognize the evolution. 

15. It is evident, therefore, that the most abiding 




Fig. 67. — Pompon anem- 
one chrysanthemum. 



252 



Plant-Breeding 



progress in the amelioration of plants must come as a re- 
sult of the very best cultivation and the most intelligent 
selection and change of seed. Every reflective person 
must admit that the cultivation of plants — which is the 
fundamental conception of agriculture — has been and is 

crude and imperfect, and that 
there has been no conscious effort 
on the part of the human race to 
produce any given final result 
upon the cultivated flora. Yet, 
this imperfect cultivation has al- 
ready modified plants so pro- 
foundly that we cannot deter- 
mine the originals of many of 
them, and we can trace the evo- 
lution of but few. The science of 
rural industry is now fairly well 
understood in its essential funda- 
mental principles, and the in- 
telligence of those classes of per- 
sons who deal with plants is 
rapidly enlarging. The first part 
of the twentieth century will vir- 
tually mark a new era for agri- 
culture, and from that time on the onward evolution 
of plants should proceed confidently and unchecked. 
Our eyes are too often dazzled by the novelties which 
suddenly thrust themselves upon us, and we look for 
some mystic power which shall enable us to produce 
varieties forthwith at our will. We need not so much 
varieties with new names as we do a general increase 




Fig. 68. — Single type. 



How Domestic Varieties Originate 



253 



. *vy|; & 



in productiveness and efficiency of the types we 
already possess ; and this augmentation must come 
chiefly in the form of a gradual evolution under the 
stimulus of good care. The man who will accomplish 
most for the amelioration and unfolding of the forms of 
plants is he who fixes his eyes steadily upon the future, 
and, with the inspiration of a long forecast, urges the 
betterment of all conditions in which plants grow. 

SPECIFIC EXAMPLES 

The foregoing principles and discussions will become 
more concrete if a few actual examples of the origination 
of varieties are given. To 
begin with a very simple 
case, we relate the intro- 
duction of the varieties of 
the dewberries, for this 
fruit is yet little cultivated, 
the varieties are few, and 
the domestication of it is 
not yet fifty years old. 

The dewberry and black- 
berry. — The dewberries 
are native fruits, and it is 
only within twenty-five 
years that they have 
become prominent among 
fruit-growers. The most 
important is the Lucretia. 
This was found growing 
wild on a plantation in 







Fig. 69. — Type of pompon chrys- 
anthemum. Grown outdoors, 
with no special care. 



254 Plant-Breeding 

West Virginia in war time. In 1876, a few of the plants 
were sent to Ohio, and from this start the present stock 
has come. It is probable that similar wild varieties are 
growing to-day in many parts of the country, but they 
have not chanced to have been seen by persons who are 
interested in cultivating them. It is a forrji of the com- 
mon wild dewberry that grows all over the Northeastern 
states. Just why this particular patch in West Virginia 
should have been so much better than the general run of 
the species nobody knows, but it was undoubtedly the 
product of some local environment or special ancestry. 

Early in the seventies, T. C. Bartel, of Huey, Clinton 
County, Illinois, observed very excellent dewberries grow- 
ing in rows between the lines of stubble in an old cornfield, 
where the plant had evidently been quick to avail itself 
of unoccupied land. This was introduced as the Bartel 
dewberry, and is now the second in point of prominence 
amongst the cultivated varieties. Other varieties have 
appeared in much the same way. A fruit-grower in 
Michigan found an extra good dewberry in a neighboring 
wood-lot, and introduced it under the name of Geer, in 
compliment to the owner of the place. In Florida an 
unusually good plant of the common wild dewberry of 
that region was discovered, and introduced by Reasoner 
Brothers under the name of Manatee. There are now 
about twenty named varieties of dewberries in cultivation 
as described in our horticultural writings, all of which, 
apparently, are chance plants from the wild. 

As the dewberries become more widely grown, good seed- 
lings will now and then appear in cultivated ground, and 
these will be named and sold. After a time persons will 



How Domestic Varieties Originate 255 

begin to sow seed for the purpose of producing new 
varieties; and those seedhngs which chance to possess 
unusual merit will be propagated, and in due time intro- 
duced. This is the history of the cultivated blackberries 
and raspberries which have come from the wild plants in 
little more than half a century. These fruits are now so 
far developed that we no longer think of looking to the 
woods and copses for new varieties of promise, yet the 
novelties are mostly chance seedlings from cultivated 
varieties. A few years ago a friend purchased plants of 
the Snyder blackberry. When they came into bearing, 
he noticed that one plant was better than the others. It 
bore larger fruits, and the bearing season was longer. He 
took suckers from this plant, and from these others were 
taken, until he had a large plantation of the novelty, 
mostly selected from plants which pleased him best. 
The variety had such distinct merit that it was named 
the Mersereau, in honor of the man who recognized and 
propagated it. 

The apple. — The original apple is not definitely known, 
but it was certainly a very small and inferior crabbed 
fruit, borne mostly in clusters. When we first find it 
described by historians, it was still of small value. Pliny 
said that some kinds were so sour as to take the edge off 
a knife. But better and better seedlings continued to 
come up about habitations, until, when printed descrip- 
tions of fruits began to be made, three or four hundred 
years ago, there were many named kinds in existence. 
The size had vastly improved, and with this increase 
came the reduction of the number of fruits in the cluster ; 
so that, at the present time, whilst apple flowers are borne 



256 



Plant-Breeding 



in clusters, the fruits are usually borne singly. That 
is, most of the flowers fail to set fruit, and they complete 
their mission when they have shed their pollen for the 
benefit of the one which persists. 

The American colonists brought with them the staple 
varieties of the mother countries. But the needs of the 

new countrj^ were unlike those 
of the old, and the tastes and 
fashions of the people were chang- 
ing. So, as seedlings came up 
about the buildings and along 
the fences, where the seeds had 
been scattered, the ones that 
promised to satisfy the new needs 
were saved, and many of the old 
varieties were allowed to pass 
away. In 1817, the date of the 
first American fruit-book, over 
sixty per cent of the varieties 
particularly recommended for 
cultivation in this country were 
of American origin. In 1845, 
nearly two hundred varieties of 
apples were described as having been fruited in this 
country, of which over half were of American origin. 
Between these two dates introduction of foreign varie- 
ties had been freely made, so that the percentage of 
domestic varieties had fallen. But the next thirty years 
saw a great change. Of 1823 varieties described in 
1872, nearly or quite seventy per cent were American, 
and a still greater proportion of the most prized 




Fig. 70. 



Japanese anemone 
type. 



How Domestic Varieties Originate 257 

kinds were of domestic origin. In the older states, the 
apple had now become so completely accustomed to its 
environment, and the tastes of the people were so well 
supplied, that there was no longer much need for the in- 




FiG, 71. — The small and regular anemone type. 

troduction of foreign kinds. It was not so in the North- 
west. There the apples of the Eastern states did not 
thrive. The chmate was too cold and too dry. Atten- 
tion was turned to other countries with similar or rigorous 

s 



258 



Plant-Breeding 



climate. In 1870, the Department of Agriculture at 
Washington imported cions of many varieties of apples 
from Russia, but these did not satisfy all fruit-growers 

of the Northern states. 
It was then conceived 
that the great interior 
plain of Russia should 
yield apples adapted to 
the upper Mississippi 
Valley, whilst those al- 
ready imported had come 
from the seaboard terri- 
tory. Accordingly, early 
in the eighties, Charles 
Gibb, of the province of 
Quebec, and Professor 
Budd, of Iowa, went to 
Russia to introduce the 
promising fruits of the 
central plain. The re- 
sults have been most in- 
teresting to the pacific 
looker-on. There are ar- 
dent advocates of the 
Russian varieties, and 
there are others who see 
nothing good in them. 
There are those who 
think that all progress must come by securing seedhngs 
from the hardiest varieties of the Eastern states ; there 
are others who would derive everything from the Siberian 




Fig. 72. 



■A pompon chrysanthemum. 
(Xi) 



How Domestic Varieties Originate 



259 



crabs; and still others who hold that the final result lies 
in improving the native crabs. There has been no end 
of discussion and cross-purposes. In the meantime, nature 
is quietly doing the work. Here is a good seedUng of some 
old variety, there a good one from some Russian, and 
now and then one from the crab stocks. The new varie- 




FiG. 73. — Type of Japanese incurved chrysanthemum. 

ties are gradually supplanting the old, so quietly that few 
people are aware of it ; and by the time the contestants are 
done disputing, it will be found that there are no Russians 
and no Eastern apples, but a brood of Northwestern apples 
that have grown out of the old confusion. 

All these new apples are simply seedlings, almost all 
of them chance trees which come up here and there 



260 Plant-Breeding 

wherever man has allowed nature a bit of ground upon 
which to make garden as she likes. In 1892, there were 
878 varieties of apples offered for sale by American nursery- 
men, and it is doubtful if one of the whole lot was the 
result of any attempt on the part of the originator to pro- 
duce a variety with definite qualities. And what is true 
of the apple is about equally true of the other fruit trees. 
In the small fruits and the grapes, where the generations 
are shorter and the results quicker, more has been done 
in the way of direct selection of seeds and the crossings 
of chosen parents ; but even here, the methods are mostly 
haphazard. Latterly, however, the professional experi- 
menters have begun the breeding of the apple and new 
varieties on a new basis have been secured ; and there is 
now considerable literature on the subject. 

Beans. — Perhaps there are no plants more tractable 
in the hands of the plant-breeder than the garden beans. 
A few years ago, a leading Eastern seedsman conceived 
of a new form of bean pod that would at once com- 
mend itself to his customers. He was so well con- 
vinced of the merits of this prospective variety, that he 
made a descriptive and ''taking" name for it. He 
then wrote to a noted bean-raiser, describing the proposed 
variety and giving the name. ''Can you make it for 
me?" he asked. "Yes, I will make you the bean," re- 
plied the grower. The seedsman then announced in his 
catalogue that he would soon introduce a new bean, and, 
in order to hold the name, he published it, along with the 
announcement. Two years later, I visited the bean- 
grower. "Did you get the bean?" I asked. "Yes, here 
it is." Sure enough, he had it, and it answered the re- 



How Domestic Varieties Originate 261 

quirements very well. Another seedsman would like a 
round-podded, stringless, green-podded bean. This same 
man produced it, and I went into a field of fifteen acres 
of it, where it was growing for seed, and the most fas- 
tidious person could not have asked for a closer approach 
to the ideal which the dealer had set before him some 
four or five years before. 

How is all this done? It looks simple enough. The 
ideal is established first of all. The breeder revolves it 
in his mind, and eliminates all the impracticable and con- 
tradictory elements of it. Then he goes carefully and 
critically through his bean fields, particularly through 
those varieties most like the desired kind, and marks 
those plants which most nearly approach his ideal. The 
seeds of these are carefully saved, and they are planted 
in an isolated position. If he finds no promising variations 
among his plantations, then he must start off the varia- 
tion in some other way. This is usually done by crossing 
those varieties which are most like the proposed kind. 
He has got a start ; but now the care and skill begin. 
Year by year he selects just those plants which please 
him best and which he judges, from experience, will most 
surely carry their features over to the offspring. He 
starts with one plant ; the next year he may have only 
two. If he has ten or twenty good ones, then the task 
is easy, for the variety has elements of permanence 
— that is, of hereditability — in it. But he may have 
no plants the second year. In that case, he begins again ; 
for if the ideal is true, it can be attained. This par- 
ticular bean-breeder upon whom many of our best seeds- 
men rely for new varieties, says that he has discarded 



262 



Plant-Breeding 



fully three thousand varieties and forms as profitless. 

This only means that he is a most astute judge of beans, 

and that he knows when any type is likely to prove to be 

a poor breeder. 

The bean also affords an excellent example of the care 

which it is generally 
necessary to exercise to 
keep any variety true to 
the type. The person of 
whom we have spoken, 
in common with all care- 
ful seed-growers, searches 
his field with great pains 
to discover the '^ rogues," 
or those plants which 
vary perceptibly from 
the type of the given 
variety. The rogue may 
be a variation in size or 
habit of plant, season of 
maturity, color or form 
of pods, productiveness, 
■^ susceptibility to rust, or 

Fig. 74. — Japanese anemone chrys- +V. K T +1 

anthemum when fully expanded. otner aberrance. Ill tne 

dwarf or bush beans, 
which are now most exclusively grown, the most fre- 
quent rogue is a climbing or half-climbing plant. This 
is a reversion to the ancestral type of the bean, which 
was no doubt a twining plant. This rogue is always 
destroyed even though it may be, itself, a good bean. 
In some cases, the men who perform the roguing are 










How Domestic Varieties Originate 263 



sent along every row of a whole field on their hands 
and knees, critically examining every plant. The effect 
of this continual selection is always to push the variety 
to greater excellence. The various 'improved" strains 
of plants are obtained in essen- 
tially this way. If the grower 
has been painstaking with his 
roguing, he soon finds that 
his seed gives better and 
more uniform crops than the 
common stock of the variety. 
If the improvement is marked, 
he may dignify his strain 
with a distinct name, and 
it thereby becomes a new 
variety The improvement 
may be a very important one 
to a careful bean-grower and 
at the same time be so slight 
as to escape the attention of 
the general farmer, or even 
of experimenters who are not 
particularly skilled in judging 
the merits of beans. 

All these examples drawn from the bean are excellent 
illustrations of the best and most scientific plant-breeding, 
and the same methods — varied to suit the different needs 
— apply to the amelioration of all other plants. The 
recent dwarf lima beans may be cited as examples of 
accidental or fortuitous varieties, in which the precon- 
ceived ideal of the plant-breeder had no place. Four 




Fig. 75. — New type wdth short 
stem, which is becoming very 
popular with commercial 
growers. 



264 



Plant-Breeding 



or five of these beans have attained some prominence. 
Henderson and Kumerle Dwarf hmas were introduced in 
1889, Burpee in 1890, and Barteldes in 1892 or 1893. 
The variety now called the Henderson was piclced up 
thirty or more years before by a negro, who found it 

growing along a roadside in Vir- 
ginia. It was afterwards grown 
in various gardens, and about 
1885 it fell into the hands of a 
seedsman in Richmond. Hen- 
derson purchased the stock of it 
in 1887, grew it in 1888, and offered 
it to the general public in 1889. 
The introduction of Henderson's 
bean attracted the attention of 
Asa Palmer, of Kennett Square, 
Pennsylvania, who had also been 
growing a dwarf lima. He called 
on Burpee, the well-laiown seeds- 
man of Philadelphia, described 
his variety, and left four beans 
for trial. These were planted in' 
the test grounds and were found 
Fig. 76. -Incurved type. ^^ ^^ valuable. Mr. Palmer's 

entire stock was then purchased, — comprising over an 
acre, which had been carefully inspected during the 
season, — and Burpee Bush lima was presented to the 
public in the spring of 1890. Mr. Palmer's dwarf lima 
originated in 1883, when his entire crop of Large White 
(Pole) limas was destroyed by cut-worms. He went 
over his field to remove the poles before fitting the land 




How Domestic Varieties Originate 265 

for other uses, but he found one Uttle plant, about ten 
inches high, which had been cut off about an inch above 
the ground, but which had re-rooted. It bore three pods, 
each containing one seed. These three seeds were planted 
in 1884, and two of the plants were dwarf, like the parent. 
By discarding all plants which had a tendency to climb, 
in succeeding crops, the Burpee Bush lima, as we now 
have it, was developed. 

The Kumerle, Thorburn, or Dreer, Dwarf lima origi- 
nated from occasional dwarf forms of the Challenger Pole 
lima, which J. W. Kumerle, of Newark, New Jersey, 
found growing in his field. The stock which came from 
these selected dwarf plants was introduced by Thorburn 
and Dreer, under their respective names. The singular 
Barteldes Bush lima came from Colorado, and is a 
similar dwarf sport of the old White Spanish or Dutch 
Runner bean. Barteldes received about a peck of the 
seed and introduced it sparingly. It attracted very little 
attention, and as the following season was dry, Barteldes 
himself failed to get a crop, and the variety was lost to 
the trade. 

Carinas. — Few plants have shown more remarkable 
evolution in very recent years than the cannas. At the 
present time, the Crozy cannas — so named from Crozy, 
of Lyons, PYance, who has introduced the greater number 
of them — are most popular. This type is often called 
the French Dwarf, or the Flowering Canna, and it is 
marked by comparatively low stature, and very large 
and showy spreading flowers in many colors, whereas 
the cannas of former years were very tall plants, with 
small and late dull red narrow flowers, and they were 



266 Plant-Breeding 

grown for their foliage effects. How has this transforma- 
tion come about? 

In the first place, it should be said that there are many 
species of canna, and about a half-dozen of these were 
well known to gardeners at the opening of last century. 
About 1830, the cannas began to attract much attention 
from cultivators, and the original species were soon 
variously hybridized. Crossed seeds, and seeds from 
the successive generations of hybrids, introduced a host 
of new and variable forms. The first distinct fashion in 
cannas seems to have been tall late-flo wiring forms. 
In 1848, Annee, a cultivator in France, sowed seeds of 
Canna nepalensis, a tall oriental species, and there sprung 
up a race of plants which has since been known as Canna 
Anncei. It is probable that this Canna nepalensis had 
become fertilized with other species growing in Annee's 
collection, very likely with Canna glauco.. At all events, 
this race of cannas became popular, and was to its time 
what the French dwarfs are to the present day. The 
plants were freely introduced into parks, beginning about 
1856, but their use began to decline by 1870 or before. 
Descendants of this type, variously crossed and modified, 
are now frequently seen in parks and gardens. 

The beginning of the modern race of dwarf large- 
flowered cannas was in 1863, when one of the smaller- 
flowered Costa Rican species (Carina Warscewiczii) was 
crossed upon a larger-flowered Peruvian species {Canna 
iridiflora). The offspring of this union came to be called 
Canna Ehemannii. This hybrid has been again variously 
crossed with other species, and modified by cultivation 
and selection, until the present composite type is the re- 



How Domestic Varieties Originate 267 






suit. Seeds give new varieties; and any seedling which 
is worth saving is thereafter multiplied by divisions of the 
root, and the resulting plants are introduced to commerce. 
The cabbage family (see Figs. 58-64).— A good illustra- 
tion of unconscious improvement is to be found in cabbage, 
kale, collard, borecale, Brussels sprouts, kohl-rabi, and cau- 
liflower. These probably came 
from a single, somewhat woody, 
branching perennial {Brassica 
oleracea) which is to be found 
growing wild on limestone bluffs 
in southwestern Europe. Some 
are a modification of the leaf, as 
in the cabbage and kale, others 
of the stem, as kohl-rabi, while 
in the cauliflower it is the selec- 
tion of the inflorescence that 
has caused the peculiar modifi- 
cation. Some of these types 
have twenty and more varieties, 
so that there are probably over 
one hundred distinct forms from 
this one wild type. All of these forms are the result of long 
and patient selection of variations that were considered 
desirable by the gardener without any conscious attempt 
to produce these specific forms. 

The chrysanthemum. —An excellent illustration of the 
appearing of a wide range of forms within the epoch of 
the systematic botanists is afforded by the florist's chrys- 
anthemum (Figs. 65-79). These chrysanthemums are now 
so widely variable and so little referable to wild species 




Fig. 77. — Hairy type. 



268 



Plant- Breeding 











that they have recently been named as a garden group- 
species, Chrysanthemum hortorum (Stand. Cyc. Hort. ii. 
755) . These plants now comprise forms sirfgle and double ; 
pompon and giant ; discoid, flat-rayed, and quilled ; ball- 
head and reflexed ; hairy-rayed ; a wide range of colors ; 
bizarre forms ; and marked differences in stature and habit 
of plant. If one were to bring together the little pompons, 
... . the hardy border types, the 

anemone-flowered, the Japanese 
incurved, and the slender singles, 
he would have difficulty in refer- 
ring them to any single origin. 

And yet the records show that 
these multitudes of forms have 
come from one oriental feral 
group, or what some botanists re- 
gard as two very similar species. 
The original was introduced to 
England about 150 years ago. 
In 1796 the Botanical Magazine figured an important large- 
flowered departure, marking the beginning, or practicaUy 
the beginning, of the modern record and development. 
The plants may have been long cultivated and consider- 
ably modified in China and Japan. What are considered 
to be the feral forms have been introduced within very 
recent years. They are most unpromising looking herbs, 
one (C. morifolium) with white rays, and the other (C. 
indicum) with yellow rays. They look no more promising 
than many weedy composites of the fields ; and yet some 
process has evolved a multitude of astonishing forms 
without our knowing how or why even though the evolu- 




FiG. 78. — Japanese type. 



How Domestic Varieties Originate 269 

tion has proceeded under our eyes and within the period 
when plants have been under close scrutiny. 



These various examples are but types of what has 
been and can be accomplished in a given group of plants. 
There is nothing mysterious 
about the subject, so far as 
the cultivator is concerned. 
He simply sets his ideal, makes 
sure that it does not contra- 
dict any of the fundamental 
laws of development of the 
plant with which he is to work, 
then patiently and persistently 
keeps at his task. He must 
have good judgment, skill, and 
inspiration, but he does not 
need genius. 

''In the improvement of 
plants," writes Henri L. de 
Vilmorin, ''the action of man, 
much like influences which act in the wild state, only 
brings about slow and gradual changes, often scarcely 
noticeable at first. But if the efforts towards the de- 
sired end be kept on steadily, the changes will soon be- 
come greater and greater, and the last stages of the 
improvement will become much more rapid than the 
first ones." 




Fig. 79. — Reflexed type. 



CHAPTER IX 



POLLINATION: OR HOW TO CROSS PLANTS 



Pollination is the act of conveying pollen from the 
anther to the stigma. It is the manual part of the cross- 
ing of plants. The word fertilization is often used in a 
like sense, although erroneously; for it is the office of 
the pollen, not of the operator, to fertilize or fecundate 

that part of the flower 
which is to develop 
into a seed. 

The structure of the 
flower. — The chief re- 
quirement in pollinat- 
ing flowers is to know 
the parts of the flower 
itself. The conspicu- 
ous or showy part of 
the flower is the envelope, which is endlessly modified in size, 
form, and color. This envelope covers the inner or essential 
organs, and it also attracts insects, which often perform 
the labor of pollination. This floral envelope is usually 
of two series or parts, — an outer and commonly green 
series known as the^calyx, and an inner and usually more 
showy series known as the corolla. These two series are 
well shown in the bellflower, Fig. 80. The calyx, with 

270 




Fig. 80. — Bellflower. 



Pollination: or How to Cross Plants 271 



its reflexed lobes, is at C, and the large bell-form part 
is the corolla. When the calyx is composed of separate 
parts or leaves, each part is called a sepal ; in like manner 
each separate part of the corolla is a petal. In the lily. 
Fig. 81, there is no distinction between calyx and corolla; 
or, it may be said, the calyx 
is wanting. These envelopes 
of the flower are often much 
disguised. This is particu- 
larly true in the orchids, one 
of which, a lady-slipper, is 
illustrated in Fig. 82. The 
sepals are seen at DD. They 
are apparently only two, but 
there is reason to believe that 
the lower sepal is really made 
up of a union of two. The 
three inner leaves are the 
petals, the lower one, H, 
being enlarged into the sac 
or slipper. 

The most important organs 
of the flower, however, to 
one who wishes to make crosses, are the so-called sexual 
organs, the stamens and pistils. They can be readily 
distinguished in the lily. Fig. 81. The six bodies shown 
at S are the ends of the stamens, or so-called male organs. 
These stamens generally have a stalk or stem, known as 
a filament, and the enlarged tip as the anther. It is in 
this anther that the pollen is borne. The pollen is usu- 
ally made up of very minute yellow or brownish grains, 




Fig. 81 . — Flower of white lily. 



272 



Plant-Breeding 



although it is sometimes in the form of a more or less 
glutinous or adhesive mass, as in the milk-weeds and 
orchids. The irritating dust which falls from the corn 
tassels at the later cultivatings is the pollen. 

The pistil, or so-called female organ, is shown at OP, 

Fig. 81. The enlarged 
portion at is the ovary, 
which develops into the 
seed-pod. The stigma, or 
the enlarged and rough- 
ened part which receives 
the pollen, is at P. Be- 
tween these two parts is 
the slender style, a part 
that is absent in many 
flowers. 

The stamens and pistils 
are known as the essen- 
tial organs of the flower, 
for, whilst the calyx and 
corolla may be entirely 
absent, either one or both 
of these organs is present ; 
and these are the parts 
that are directly concerned in the reproduction of the species. 
Like the floral envelopes, these essential organs are often 
modified, so much so that botanists are sometimes perplexed 
to distinguish them from each other or from modified forms 
of the petals or sepals. The particular features of these 
organs which the plant-breeder must be able to distin- 
guish are the anther and the stigma ; for the anther bears 




Fig. 82. 



— Flower of greenhouse 
cypripedium. 



Pollination: or How to Cross Plants 273 

the pollen and the stigma must receive it. In Fig. 80, the 
stamens are shown at E. In the flower A, which has just 




Fig. 83. — Flower of night-blooming cereus. 



expanded, these stamens are rigid and in condition to 
shed the pollen, but in the flower B, they have shed the 
pollen and have collapsed. The stigma in this case is 

T 



274 



Plant-Breeding 



divided into three parts, but when the flower first opens, 
these parts are closed together, H in flower A, so that it 
is impossible that they receive any pollen from the same 
flower; when the stamens have withered, however, as in 
B, the stigma, H, spreads open and is ready to receive 
any pollen which may be brought to it by insects or 




Fig. 84. — Flower of the shrubby hibiscus {Hibiscus syriacus). 



other agencies. In this case, the ovary or young seed-pod, 
which is in the bottom of the flower, is not shown in the 
engraving. 

Some of the particular forms of essential organs are 
well illustrated in the accompanying photographs. In 
the night-blooming cereus, Fig. 83, the many-rayed stigma 
is shown just below the center of the mouth of the flower, 



Pollination: or How to Cross Plants 275 



and the numerous stamens are 
arranged in a circular form out- 
side of it. The many petals and 
numerous spreading sepals are 
also well shown. The hibiscus, 
Fig. 84, has a central column 
with the anthers hanging upon 
it, and a large stigma raised 
beyond them. The wild bug- 
bane, or cimicifuga, is seen in 
Fig. 85, natural size. Here fs a 
long spike or cluster of flowers. 
At the top are the unopened 
buds, in the center the expanded 
flowers with the floral envelopes 
fallen away, — the fringe-like 
stamens very prominent, — and 
below are seen the pistils, the 
stamens having fallen. These 
pistils will now ripen into pods, 
but the tip-like stigma may still 
be seen on them. The stamens 
and the long protruding style 
are also shown in the fuchsia. 
Fig. 94. The essential organs 
of orchids are curiously dis- 
guised. They are combined into 
a single body. In the lady-slip- 
per, Fig. 82, the lip-like stigma 
is shown at P. On either side, 
at its base; is an anther, S. Pro- 




FiG. 85. — Bugbane {Cimici- 
fuga racemosa). 



276 



Plant-Breeding 



jecting over the stigma is a greenish ladle-Hke body, T, 
which is a transformed and sterile anther. In all lady- 
slippers, these organs are essentially the same as in the 
drawing, although they vary much in size and shape ; 
but in most other orchids, the two side anthers, S, are 

wholly wanting, 
and the terminal 
organ, T, is a 
pollen-bearing 
anther. In nu- 
merous plants, 
there are many 
distinct pistils 
in each flower. 
Such is the case 
in the straw- 
berry, where 
each little yellow 
''seed" on the 
ripened berry 
represents a pis- 
til ; and the 
blackberry and 
the raspberry, 
where each little grain or drupelet of the fruit stands 
for the same organ. A flowering raspberry is illustrated 
natural size in Fig. 86, for the purpose of showing the 
ring of many anthers near the center of the flower, inside 
of which, in the very center, is a little head of pistils. 

It frequently occurs that the stamens and pistils are 
borne in different flowers, rather than together in the 




Fig. 



86. — Blossom of flowering raspberry 
(Rubus odoratus) . 



Pollination: or How to Cross Plants 277 

same flower, as they are in the examples we have studied. 
In these cases the flower is said to be staminate, or 
male or sterile, in one case, and pistillate, female or fer- 




FiG. 87. — Squash flowers of each sex. 

tile, in the other case. If these two kinds of flowers are 
borne together on the same plant, as in pumpkins, 
melons, cucumbers, chestnuts, oaks, and begonias, the 
plant is said to be monoecious; but if the staminate and 



278 • Plant-Breeding 

pistillate flowers are on entirely different plants, as in 
willows and poplars, the plant is dioecious. The two kinds 
of squash flowers are shown in Fig. 87. The pistillate 
flower is on the left, and it is at once distinguished by the 
ovary or little squash below the colored part, or corolla 
of the flower. The lobed stigma is seen in the center. 
The staminate flower is on the right. It has a longer 



HIH 


■■ 


imHP^^'^^sn 


H^^^H 


■ ^ 


^^^^^^^N^^^^^jHjSSH 


igPf 




^ ^gj^^^^ ^-J^^^'. ^•'^'^^v^''^-' ■'3 


H 


^£^^ 




&X^ 


h' -"Jl^Km 




B^"^ 


HJ^l 


B ^^' ■ ^'"^^^MH 


!sS. 


mk 


I^H^n^^HK. "^'^ J^^^^^^^^^H 



Fig. 88. — Flowers of clematis {Clematis virginiana) . 

stem, no ovary, and the anthers are united into a con- 
spicuous cone in the center. The flowers expand early 
in the morning. Insects carry pollen to the pistillate 
flower, which then begins to set its fruit, whilst the 
staminate flower dies. The flower of the common wild 
clematis is shown in Fig. 88. On the right are the 
sterile flowers, which are wholly staminate. On the left, 
the flowers with larger sepals — the petals are absent — 
have a cone of pistils in the center, and a few short and 



Pollination: or How to Cross Plants 279 

sterile stamens spreading from the base of the cone. 
These different flowers are borne on different plants in 
this species of clematis, and the plants are therefore 
practically dioecious, because the stamens of the pistillate 
flowers generally bear no pollen. A similar mixed ar- 
rangement occurs in some strawberries, except that there 
are no purely staminate flowers. There are purely pistil- 
late varieties, others, as the Crescent, with a few nearly 
or quite abortive stamens at the base of the cone of pistils, 
and others in which the flowers are perfect or hermaph- 
rodites, that is, containing the two sexes. 

The compositous flowers — as the asters, daisies, golden- 
rods, sunflowers, dahlias, zinnias, chrysanthemums, and 
their kin — need to be considered in still a different 
category. In these plants, the head, or so-called flower, 
is an aggregation of several or many small flowers or 
florets. Each seed in a sunflower head, for example, 
represents a distinct flower. Sometimes all of these flowers 
are perfect, — contain the two sexes, — and sometimes 
they are pistillate or staminate in different parts of the 
head; and in some cases the plants are dioecious. In 
many plants of the composite family, the flowers near the 
border of the head are unlike those of the center or disk, 
in having a long ray-like corolla; and these ray-flowers 
are frequently of different form from the others in the 
character of the essential organs. Very frequently the 
ray-flowers are pistillate, whilst the disk flowers are 
generally hermaphrodite. The anthers in these plants 
are united in a ring closely about the style and below the 
stigma. 

The ovary, as we have seen, ripens into the pod, berry. 



280 Plant-Breeding 

or other fruit ; but it is not able to bear seeds until it is 
assisted by the pollen. The pollen falls upon the roughish 
or sticky surface of the stigma, and there germinates or 
sends a minute tube downwards through the style and 
finally reaches the ovule, which, when fertihzed, rapidly 
ripens into the seed. The nature of this fecundation is 
not germane to the present subject ; but it may be said 
that only one pollen-grain is necessary to the fertilization 
of a single ovule, but the addition of a superabundance 
of pollen greatly stimulates the growth of the fleshy or 
enveloping parts of the fruit. It is important that the 
person who desires to cross plants should become familiar 
with the stigma when it is ''ripe," receptive, or ready to 
receive the pollen. This condition is usually indicated 
by the glutinous or sticky or moist condition of the stigma, 
or in those stigmas which are not glutinous it is told by 
the appearing of a distinctly roughened or papillose 
condition. This receptive condition generally occurs 
about as soon as the flower opens. If pollen is withheld, 
the stigma will remain receptive much longer than when 
fertilization has taken place, — in some flowers for two 
or three days. 

The pollen is discharged from the anther in various 
ways, but it most commonly escapes through a chink or 
crack in the side of the anther. Sometimes it escapes 
through pores at one end of the anther ; and in other 
cases there are more elaborate mechanisms to admit of 
its discharge. In most plants, the anthers and stigma 
in the same flower mature at different times, so that 
close-fertilization or in-breeding is avoided. This is 
well illustrated in the bellflower. Fig. 80. Here the anthers 



Pollination: or How to Cross Plants 281 

wither and die before the stigmatic lobes open. In other 
cases, the stigma matures first, although this is not the 
usual condition. 

Manipulating the flowers. — We are now familiar with 
the essential principles in the pollination of flowers. 
Before a person proceeds to operate on a flower with which 
he is unfamiliar, he should carefully study its structure, 
so as to be able to locate the different organs, and to dis- 
cover when the pollen and the stigma are ready for work. 

The first and last rule in the pollinating of plants is this : 
Exercise every precaution to prevent any other pollina- 
tion than that which you design to give. The anthers, 
therefore, must be removed from the flower before it 
opens. This removal of the anthers is known as emascula- 
tion. Just as soon as this is done, tie up the flower securely 
in a bag to protect it from foreign pollen, which may be 
brought by winds or insects. As soon as the stigma is 
ripe, remove the bag and apply the desired pollen, placing 
the bag on the flower again, where it must remain until 
the seeds begin to form. The stigma may be receptive 
the day following emasculation, or, perhaps, not until a 
week afterwards. Much depends on the age of the bud 
when emasculation takes place. It is commonly best 
to delay emasculation as long as possible and not have 
the flower open ; but the operator must be sure that 
the anthers do not discharge or that insects do not get 
into the flower before he has emasculated it. The bud at 
B, in Fig. 82, is nearly ready to emasculate. The older 
buds on the top of the spike of bugbane. Fig. 85, are 
ready to operate ; and so is the bud seen at the left in 
Fig. 86. 



282 



Plant-Breeding 



The manner of emasculating the flower varies with the 
operator. It is a common practice to cUp off the anthers 
with a pair of small scissors, or to hook them out with a 
bent pin or a crochet hook. There are disadvantages 
in any of these methods, because the anthers are hkely 




Fig. 89. — Tobacco flowers, showing the parts of the flower, a bud ready 
to be emasculated, and an emasculated subject. 



to drop into the bottom of the corolla, where it is some- 
times difficult to rescue them ; and if one uses tweezers, 
there is always danger that the anthers may be crushed 
and that some of the pollen may adhere to the instrument 
and contaminate future crosses. We may therefore cut 
the corolla completely off just above the ovary, with a 



Pollination: or How to Cross Plants 283 

pair of small, long-handled surgeon's scissors (see Fig. 
91), removing everything but the pistil. The operation 
is explained in Fig. 89, which shows the tobacco flower. 




Fig. 90. — Zinnia flowers ; the upper head ready for emasculation, the 
lower one showing the operation performed. 



The flower at the left shows the pin-head stigma in the 
center of the throat, and the five anthers surrounding 
it. The second flower is spread open for the purpose 
of showing these organs. The third figure is a bud in 



284 



Plant-Breeding 




Fig. 91. — liisULuueiiis UMti 111 pollinating flowei.-«, iiatural size. Pin 

scalpel, scissors, lens. 



the right condition for operation. The right-hand figure 
shows this bud cut around with the points of the scissors, 



Pollination: or Hov) to Cross Plants 285 

leaving only the pistil. The line at W, in Fig. 81, shows 
where the flower of the lily might be cut off. 

The method for a compositous flower is shown in the 
picture of the zinnia, Fig. 90. In this plant the outer 
flowers of the head are pistillate, whilst those of the 
disk are perfect. It is only necessary, therefore, to remove 
the central stamen-bearing flowers before any of them 
open, and to cover the flower up before any of the pistils 
near the border have protruded themselves. The upper 
head in Fig. 90 shows the untreated sample, while the 
lower one shows the same with the cone of central flowers 
puUed out. This treated head should now be covered, 




Fig. 92. — Ladle for pollinating house tomatoes. 

to await the maturing of the stigmas. In many composi- 
tous plants, however, the case is not so simple as this, 
because all the flowers are perfect. In such cases, nearly 
all the florets should be removed from the head, and a 
few remaining ones emasculated in essentially the same 
method as described for the tobacco, Fig. 89. 

Whenever flowers are borne in clusters, nearly all of 
them should be removed and the attention confined to 
Only two or three of them. One is then more certain of 
getting seeds to set. In some cases, like the apple cluster, 
only one or two flowers of any cluster ever set fruit, 
and the operator should then choose the two or three 
strongest and most promising buds, and cut all the others 
off. 



286 



Plant-Breeding 



Flowers that bear no stamens, as the pistillate flowers 
of squashes, strawberries, and many other plants, of 
course do not require emasculating. They should ]:>e 
tied up while in bud, however, to prevent the access of any 
foreign pollen. Indian corn is a case in point. The 

pistillate flowers are on the ear, each 
kernel of corn representing a single 
flower. The silks are the stigmas. 
If it is desired to cross corn, there- 
fore, the ear should be covered before 
any silks are protruded, and the 
pollen should be applied some days 
later, when the silks are fully grown. 
The staminate or male flowers are 
in the tassel. 

The pollen should be derived from 
a flower which has also been pro- 
tected from wind and insects, be- 
cause foreign pollen may have been 
dropped upon an anther by an insect 
visitor, and it may be unknowingly 
transferred by the operator. The 
pollen-bearing parent needs no oper- 
ation, of course, but the flower should have been tied up in 
a bag when it was in bud. The pollen is best obtained by 
picking off a ripe anther and crushing it upon the thumb- 
nail. Then it is transferred to the stigma by a tiny scalpel 
made by hammering out the small end of a pin, as shown, 
full size, at the left in Fig. 91. The stigma should be 
entirely covered with the pollen, if possible. It is often 
advised to use a camel' s-hair brush to transfer pollen, 




>3 — ^^"■^f^ 



Fig. 93. — Bag for cov 
ering the flowers. 



Pollination: or How to Cross Plants 287 

but much of the poUen sticks amongst the hairs of the 
brush and is ready to contarninate a future cross ; and 
when the pollen is scarce it cannot be conserved to ad- 




FiG. 94. — Fuchsias, showing the stainens and pistils, and a bud ready 

to be emasculated. 



vantage by a brush. In some cases the pollen is discharged 
so freely that the anther may be rubbed upon the stigma, 
or even shaken over it, but in most instances it will be 



288 



Plant-Breeding 



necessary actually to place the pollen upon the stigma 
with some hand instrument. When pollinating house- 
grown melons and cucumbers, the staminate flower is 
broken off, the corolla stripped back, and the anther- 
cone inserted into the pistillate flower, where it is allowed 
to remain until it dries and falls away. In pollinating 
house tomatoes, an implement shown in Fig. 92, one-third 
size, is used. This is simply a watch-glass, T, secured to a 




Fig. 95. — Fuchsia flower emasculated. 



handle. When the house is dry, at midday, the watch- 
glass is held under the flowers, which are tapped, and the 
pollen falls into the glass. The glass is then held up 
under another flower until the stigma rests in the pollen. 
It should be said, however, that this pollination of toma- 
toes is for the purpose of making the fruit set in the ab- 
sence of insects, not to effect a cross. If the latter pur- 
pose were the object sought, the flowers which are to 
bear the seeds would need to be emasculated. 



Pollination: or How to Cross Plants 289 



Sometimes it is im- 
possible to secure the 
pollen at the time the 
stigma is ready. In 
some cases of this kind, 
the intended parents can 
be grown under glass so 
as to bring them into 
bloom at the same time. 
In other cases, it is nec- 
essary to keep the pollen 
for some time. The 
length of time that pol- 
len will keep varies with 
the species and probably 
also with the strength 
and vigor of the plants 
that bear it. As a rule, 
it will not keep more 
than a week or two, 
and, in general, it may 
be said that the fresher 
it is, the better it may 
be expected to act. It 
is best kept in dry and 
tight paper bags, such 
as are used for covering 
the flowers. 

Something more should be said about the bags which are 
used for covering the flowers. It has been found that 
light transparent oiled paper bags are the best. For 




Fig. 96. 



Fuchsia flower tied up after 
emasculation. 



U 



290 



Plant-Breeding 



small flowers use the two-ounce bags and for larger flowers 
use the four-ounce size. If oiled bags are not available, 
the ordinary manilla bags may be used. When they are 
still flat, as they come from the packages, a hole is made 
near the opening, and a string is passed through it and 
then tied at one of the folds, as shown in Fig. 93. The 
bag is then ready for use. Before it is put on the flower, 
the lower end of it is dipped in water to soften it so that 




Fig. 97. — Tomato and quince, showing how the sepals were cut off 

in emasculating. 



it can be puckered tightly about the stem and thereby 
prevent the entrance of any insect. A bag is put upon 
the seed-bearing flower when emasculation is performed, 
and upon the intended pollen parent when the flower is 
still in bud. The bag may be removed from the emas- 
culated flower from time to time to examine the stigma, 
and again when the pollen is applied ; but it should 
not be taken off permanently until the pod or fruit 
begins to grow. 

By way of recapitulation, let us consider the crossing 



Pollination: or How to Cross Plants 291 



of a fuchsia flower. In Fig. 94 two flowers are shown in 
full bloom, with the long style and the eight shorter sta- 
mens. The single bud is just the right age to emasculate. 
We therefore cut off the two flowers and emasculate the 
bud, as in Fig. 95. The pollen of another flower is apphed 
and the bag is tied on, as seen in Fig. 96. The best label 
is a small merchandise tag, and this records the staminate 
parent and the date. 

It will be seen that in 
the operation of emas- 
culating the fuchsia 
flower- we cut off the 
sepals as well as the 
petals. In some plants 
the calyx adheres- to 
the full-grown fruit, 
as on the apple, pear, 
quince, gooseberry, or 
persists at the base 
of the fruit, as in the 
tomato, pea, raspberry. 
In these fruits, there- 
fore, the cutting away 
of the calyx leaves an 
indelible mark which 




Fig. 98. — Pollinating kit. 



, at once distinguishes the fruits which have been crossed, 
even if the labels are lost. In Fig. 97 a tomato and quince 
are shown thus marked. 

All the foregoing remarks do not apply to the crossing 
of ferns, lycopodes, and the like, because these plants 
have no flowers; yet cross-fertilization may take place 



292 



Plant-Breeding 




in them. When the spores of these flowerless plants are 
sown, a thin green tissue, or prothallus, appears and 
spreads over the ground. In this tissue the separate 
sex-organs appear, and after fecundation takes place, 
the fern, as we commonly understand it, springs forth. 
Thereafter, this fern lives an asexual life and produces 
spores year after year ; but it is only in this primitive 
prothallic stage that fertilization takes place, once in the 

life time of the plant. 
If these plants are to 
be crossed, the only 
procedure open to the 
gardener is to sow the 
spores of the intended 
parents together in 
Fig. 99. — Pollinating kit. the hope that a nat- 

ural mixing may take 
place. There are various well-authenticated fern hy- 
brids. 

The pollination of flowers is such a siniple work that 
few implements are required for its easy performance. 
Great care is more important than any number of tools. 
Every one who expects to cross plants should provide him- 
self with the three instruments shown in Fig. 91, — a pin 
scalpel, sharp-pointed scissors, and a large hand-lens. If 
one contemplates much experimenting in this direction, 
however, it is economy of time to have some sort of box 
in which there are compartments for the various necessi- 
ties. These various compartments suggest at once whatever 
accessories are wanting, and they hold a sufficient supply 
for several hundred operations. There should be a com- 



Pollination: or How to Cross Plants 293 

partment for bags, string, lens, scissors, and pencils, tags, 
note-book, and the like. Figs. 98 and 99 show a con- 
venient case for an experimenter, and one that has been 
used with satisfaction for several years. This kit is 
twelve inches long, nine inches wide, and three inches 
deep. 



CHAPTER X 

THE FORWARD MOVEMENT IN PLANT- 
BREEDING 

The first specific interest in cultivated plants was in 
the gross kinds or species. As the contact with plants be- 
came more intimate, various indefinite form-groups were 
recognized within the limits of the species. Gradually, 
with the intensifying of domestication and cultivation, 
very particular groups appeared and were recognized. 
These smaller groups came finally to be designated by 
names, and the idea of the definite and homogeneous 
cultural variety came into existence. The variety-con- 
ception is really a late one in the development of the human 
race. It is practically only within the past two centuries 
that cultivated varieties of plants have been recognized 
as being worthy of receiving designative names. It is 
within this period, also, that most of the great breeds of 
animals have been defined and separately named. 

All this measures the increasing intimacy of our contact 
with domesticated plants and animals. It is a record 
of our progress. The peoples that are most advanced in 
the cultivation of any plant are the ones that have the 
most named varieties of that plant. In Japan, to this 
day, the plums are said to pass under ill-defined class 

294 



The Forward Movement in Plant-Breeding 295 

names. We have introduced these classes, have sorted 
out the particular forms that promise to be of value to us, 
and have given them specific American names. Some time 
ago a native professor in Japan wrote me asking for cions 
of these plums, in order that he might introduce Japanese 
plums into Japan. The Russian apples are designated to 
some extent by class names ; in fact, it was not until the 
appearance of Kegel's work, about a generation ago, that 
Russian pomology may be said to have begun. What 
constitutes a variety is increasingly more difficult to define, 
because we are constantly differentiating on smaller 
points. The growth of the variety-conception is really 
the growth of the power of analysis. 

The earlier recognized varieties seem to have come into 
existence unchallenged. There is very little record of 
inquiry as to how or why or even where they originated. 
That is, the quest of the origin arose long after the 
recognition of the variety as a variety. Even after 
inquisitive search into origins had begun, there was Httle 
effort to produce these varieties. The describing of varie- 
ties and the search into their histories was a special work 
of the nineteenth century. One has only to consult such 
American works as Downing's ''Fruits and Fruit Trees 
of America," and Burr's ''Field and Garden Vegetables of 
America," to see how carefully and methodically the 
descriptions and synonymy of the varieties were worked 
out. These are types of excellent pieces of editorial and 
formal systematic work. 

Systematic improvement of plants. — There have been 
isolated efforts at producing varieties for many years. 
These efforts began before the time of the general discus- 



296 Plant-Breeding 

sion of organic evolution. In fact, it was on such experi- 
ments that Darwin drew heavily in some of his most 
important writing. Roughly speaking, however, the 
conception that the kinds of plants can be definitely modi- 
fied and varied by man is a product of the last half century. 
We now think that there is such a possibility as plant- 
breeding. It is really a more modern conception, so far 
as its general acceptance is concerned, than animal- 
breeding. But both animal-breeding and plant-breeding 
are the results of a new attitude toward the forms of 
life — a conviction that the very structure, habits, and 
attributes are amenable to change and control by man. 
This is really one of the great new attitudes of the modern 
world. 

The term plant-breeding itself is new. It occurs only 
in the most recent supplements of dictionaries. Before this 
term came into use, such words as ''improvement" and 
''amelioration" of plants were employed, although cross- 
breeding had long been current. The early writings of 
Verlot and Carriere were under the title of " production 
and fixation of varieties of plants." The term plant- 
breeding carries the conception of a definite purpose in the 
producing of new forms and attributes of plants, by cross- 
ing, selection, and whatever other means may be useful. 

One of the "signs of the times" in North America is the 
attention that is being given to the practical breeding of 
plants. A host of persons is actually at work. There 
are professorships devoted to the subject. Many societies 
are giving special attention to the practical improvement 
of plants. Results are accumulating rapidly with very 
many kinds of plants, and the literature is growing rapidly. 



The Forward Movement in Plant-Breeding 297 

Eventually, of course, we shall be able to formulate 
somewhat definite statements as to how to proceed to 
secure desired results, and then the literature of plant- 
breeding can be intelligently rewritten. However, there 
is no hope that plant-breeding can ever proceed with such 
exactness as to enable us to produce forthwith the things 
that we desire, in the way in which the mechanician devises 
new machines, notwithstanding all the suggestions of 
persons who write with much self-assurance. For all 
that we can now see, plant-breeding will always be an 
experimental process. It is this very experimental 
uncertainty of the work that gives it much of its charm to 
inquisitive and sensitive minds. 

The plant-breeder should aim toward definite ideals. — 
Now, plant-breeding is worthy of the name only as it sets 
definite ideals and is able to attain them. Merely to 
produce new things is of no merit ; that was done long 
before man was evolved. A child can '^ produce" a new 
variety, but it may learn nothing and contribute nothing 
in producing it. In many ''new" things that are pro- 
duced there may be dispute as to whether they are new, 
and as to whether they are distinct enough to be named 
and therefore to be ranked as varieties at all. This is not 
science, nor even breeding : it is playing and guessing. 
What does the world care whether John Jones produces 
''Jones' Giant Beardless Wheat" ? But it does care if he 
produces wheat having a half of one per cent more protein. 
We must give up the production of mere "varieties" ; we 
must breed for certain definite attributes that will make 
the new generation of plants more efficient for certain 
purposes : this is the new out-look in plant-breeding. 



298 Plant-Breeding 

Plant improvement a serious business. — In considering 
the American achievement in plant-breeding, we must 
divest ourselves at the outset of all idea of "wonder," and 
"miracle," and other nonsense, which has been so much 
written into the subject in very recent time. Plant- 
breeding is a plain and serious business, to be conducted 
by carefully trained persons in a painstaking and method- 
ical way. It is not magic. There are persons who have 
unusual native judgment as to the merits and capabilities 
of plants and who develop great manual skill ; but they 
are plain and modest citizens, nevertheless, and their 
methods are perfectly normal and scrutable. The wonder- 
mongers are the reporters, not the plant-breeders. 

It is a curious psychological phenomenon that the popu- 
lace, or a certain part of it, seems to lose its head now and 
then. This phenomenon is not peculiar to politics. It 
enters those domains that are compassed by fact and that 
in ordinary times are dominated by common sense. 
Plant-breeding has been seized of this sensationalism. 
Newspapers, magazines, and books have spread the most 
wonderful tales. The lay writers have at last awakened 
to the fact that great progress is making in agricultural 
subjects, and, with a fragmentary and superficial view 
here and there, have written of the subjects with all the 
enthusiasm and partiality of new discovery. We have 
now in mind not only the inflated writing about plant- 
breeding, which constitutes a regrettable contribution to 
current horticultural literature, but also that general 
tendency to exploit everything that is capable of high 
coloring. The agricultural historian, when he takes ac- 
count of the exploitations of the present day, will recall other 



The Forward Movement in Plant-Breeding 299 

stages in which we seem temporarily to have lost our better 
judgment, of which the Morus multicaulis craze and the 
lightning-rod boom are examples in two past generations. 

Having now warned our readers that we have nothing 
, marvelous in store, we shall proceed to indicate some of 
the ways in which American plant-breeders are working, 
fully conscious that the space at our disposal is much 
too httle to allow of any adequate presentation of the 
subject. It may not be out of place to call the reader's 
attention to the three foundations on which rests the in- 
creased productiveness of crops and animals : — 

The enrichment of the land; 

The tillage and care ; 

The producing of better varieties and strains. 

We have long given careful attention to the first two ; 
now we are studying the third with new enthusiasm aad 
purpose. 

The results of pla7it-hreeding effort. — Happily, we are 
not without abundant accompHshment in this new field. 
The last ten years has seen a remarkable specialization 
in the producing of plants that are adapted to particular 
needs. The days of merely crossing and sowing the 
seeds to see what will turn up are already past ^dth 
those who are engaged seriously in the work. The old 
method was hit-and-miss, and the result was to take 
what good luck put in our way : the new method proceeds 
definitely and directly, and the result is the necessary 
outcome of the Hne of effort. The crux of the new ideal is 
efficiency in one particular attribute in the product of 
the breeding. These attributes are measurable; the 
kinds of results are foreseen in the plan. 



300 Plant-Breeding 

State plant-breeding associations. — One of the most 
significant advances in popular interest in plant improve- 
ment is the banding together of persons in many of the 
states and provinces in an organized effort to improve 
plants, especially field crops. This line of effort has been 
largely brought about at the suggestion of some officer 
of the state agricultural college, who is often an expert 
plant-breeder himself, and usually acts as secretary of the 
association. These associations have done great good 
in arousing interest in plant-breeding. 

The Wisconsin Association, known as the Wisconsin 
Agricultural Improvement Association, was estabhshed 
Feb. 22, 1901, and now has a paid-up membership of 
over 2000 persons, consisting of '^all former, present, and 
future students and instructors of the Wisconsin College 
of Agriculture," also ''any person residing within the state 
having completed a course in agriculture in any college 
equivalent to that given by the Wisconsin University." 
More recently the county agricultural schools have been 
admitted to membership and honorary members may be 
elected by a majority vote at any annual or special meet- 
ing of the association. 

The association has organized some 44 county sub- 
orders, which are smaller units conducting an active 
work in more restricted areas. These county orders con- 
tain approximately 4000 members. Any one interested in 
agriculture may unite with the county order. They have 
become live centers which stand behind all agricultural 
activities and lend a helping hand in making agricultural 
and other resources of the county known far and near. 
As a result of the association there has been established 



The Forward Movement in Plant-Breeding 301 

in the neighborhood of 2000 seed-grain centers where 
pure-bred seed barley may be obtained. It is estimated 
that over seventy-five per cent of the seed barley of Wis- 
consin is of one distinct variety. 

Another series of organizations, to be known as 'Hown- 
ship organizations," has been planned. These are smaller 
groups within the county orders. Three are already in 
existence. This scheme of organization brings the activi- 
ties of the association to practically every farmer of the 
state. 

Starting out primarily as breeding associations, their 
activities have extended in many directions. An alfalfa 
order has been established which is closely affiliated with 
the main association : its object is 'Ho promote the alfalfa 
interests of the state in general," 

1st. By cooperating with the Department of Agronomy 
and the Wisconsin Agricultural Experiment Association 
in growing, experimenting, and in the wide dissemination 
of alfalfa ; 

2d. By having alfalfa exhibits at agricultural fairs ; 

3d. By having annual meetings in order to report and 
discuss topics beneficial to the members of the order ; 

4th. By distributing Uterature and information bearing 
upon the production of alfalfa for seed and forage. 

The alfalfa order was organized three years ago and now 
has a membership of 1200. In 1914, 50 tons of alfalfa 
seed were sent out for experimental purposes. 

The association receives state aid, $5000 a year, and 
some of the county orders receive financial aid from the 
county. The annual dues of members is fifty cents. 

One of the principal aims of the Wisconsin association 



302 Plant-Breeding 

is to place pure-bred seed on the market. This seed is 
to bear the seal of the association. 

It is estimated that members of the association sell 
over three hundred thousand dollars' worth of pure-bred 
seed a year. The members are in close touch with the 
breeding work of the experiment station and test, propa- 
gate, and disseminate the improved grains which are pro- 
duced on the station farm. 

The association prints an annual report of over one 
hundred pages containing the progress of the members in 
improving seed grain and much valuable information 
concerning plant-breeding in general. Such titles as the 
following appear in recent annual reports : — 

Dissemination of Pure Bred Seed Grains, Through the Coopera- 
tion of Students in the Country Schools, J. C. Brockert. 

Necessity of Thorough Preparation of Pure Bred Seed Grain for 
the General Trade, Wm. R. Leonard. 

County Order of Experiment Association as Factor to Promote 
Dissemination of Pure Bred Grain, R. A. Moore. 

Importance of Testing Our Pure Seed Grains Previous to Sowing 
Season's Crop, H. L. Post. 

Importance of the Farm Inspection Work, and How Shall It Be 
Carried Out? E. B. Skewes. 

Growing and Preparing Seed Grains and Forage Plants for 
Exhibition, O. R. Frauenheim. 

Wheat Breeding — The Value of the Individual, F. H. Demaree. 

In this connection, mention should be made of the 
Wisconsin Potato Growers' Association, an active and 
growing organization whose object is to improve the seed 
and table potatoes of Wisconsin by breeding and to 



The Forward Movement in Plant- Breeding 303 

guarantee variety shipments true to name and free from 
disease. This association, Uke its sister organization, does 
business on a large scale and has at present nearly 300 
members. '' Potato Special " trains have been run through- 
out the state under its auspices and that of the State 
College of Agriculture, and several very successful potato 
exhibits have been held. 

This association has done much to standardize certain 
commercial varieties of potatoes and to put seed on the 
market which is true to name. Its members found our 
varieties badly mixed up and containing many distinct 
types. This purifying of varieties is the first step toward 
careful and systematic breeding. 

A Minnesota association, known as the ''Minnesota 
Field Crop Breeders' Association," has been organized 
with a similar plan and objects as the Wisconsin associa- 
tions. It publishes an elaborate annual report giving 
information concerning the work of the association as a 
whole and the activities of the county sections, of which 
there are many. One of the functions of the association, 
besides encouraging the production and sale of pure-bred 
seeds, is to stage elaborate exhibits of farm products at 
the state and other fairs. 

In some states, notably lUinois, Ohio, and New York, 
associations of breeders have been established on a dif- 
ferent membership basis. They have chosen to have 
smaller associations consisting of persons who bind them- 
selves to follow certain rules and regulations laid down 
by the association. The IlUnois Seed-corn Breeders' 
Association is such an organization. Its members grow 
certain varieties of corn recognized by the association 



304 Plant- Breeding 

and offer these for sale with the approval and backing of 
the association. 

The Ohio and New York associations laid out elabo- 
rate plans of breeding for their members to follow, but it 
was found that farmers were not ready for such work and 
as a result the Ohio association has never been very large 
and the New York association has abandoned this plan 
and is turning its attention to bringing the farmers and 
seedsmen into closer relations, encouraging the farmer to 
demand a better product and the seedsmen to produce one. 

Other plant-breeding associations. — The most notable 
breeders' associations are the Canadian Seed Growers' 
Association and the Swedish Seed Association. 

The former has an elaborate system of inspection of all 
seeds sold by members of the association under the su- 
pervision of a permanent, salaried secretary. The results 
are noteworthy. The standard of seed grain has been 
tremendously raised in Canada and much better crops 
are the result. Canadian seed grain is now in demand 
all over the world. The Canadian experiment stations 
are leading in this work by carefully and systematically 
producing improved varieties on their experimental farms 
and distributing them to members of the association who 
grow them, keeping up a careful selection from year to 
year and offering them for sale. 

The Swedish association has an interesting history and 
an enviable record. It has done more, probably, than 
any other organization to reshape our conception and 
methods of selection. Dr. Nilsson and his associates 
have started on a large scale the principle of individual 
selection in contrast to the older method of mass selection 



The Forward Movement in Plant- Breeding 305 

which is now largely given up. The group of scientists 
at Svalof have not only shown their ability to produce 
practical results, but they have also elaborated scientific 
principles. 

The founding of the station at Svalof is wholly due to 
the private initiative of a group of Swedish farmers. The 
purpose of the association has always been to produce 
practical results, to breed better grains for local use. 

But the station has been fortunate from the first in 
having in its employ expert botanists whose skill has not 
only produced many noteworthy new varieties, but who 
have elaborated scientific principles of far-reaching im- 
portance. These men have been given a free hand to 
pursue their work without such distracting activities as 
teaching, comparative field trials, commercial analyses, 
and the like. This fact together with an unrestricted 
organization, a well-selected program, and an expert corps 
of assistants accounts for the wonderful success of this 
station. 

This Swedish seed association has two groups of mem- 
bers: those who are permanent after having paid $28 
once for all ; and those who pay annually $1.40. 

The association has an annual budget of about $40,000 
derived from dues of members, contributions from agri- 
cultural associations, government aid, and sale of pedigreed 
seed. Funds from the last two sources have increased 
very rapidly in recent years. Gifts of various kinds 
amounting to $77,000 have been set aside for buildings. 

Accordingly, the society now has at its disposal a large 
and well-equipped establishment, comprising two con- 
nected buildings serving as laboratories (Fig. 100), a house 



306 



Plant-Breeding 




The Forward Movement in Plant-Breeding 307 

for preparatory work, with a little farm and a dwelling 
house ; it also owns 40 acres of land, of which special 
cultures and seed multiplication plots occupy 25 acres. 
Despite this, it has been found necessary to make most 
of the cultural experiments on the wide fields of the huge 
property adjoining, in order to give the different cereals, 
occupying in all about 30 acres a year, their proper place 
in the rotation of crops, which is found absolutely neces- 
sary for a normal development. 

The program of work in Sweden was, at first, vague 
and uncertain. Theorizing scientists were attempting to 
solve problems for practical farmers and nobody had 
blazed the trail. The starting-point of the work was 
naturally the method of selection in vogue at the time, 
that is, the Darwinian method of ''methodical selection" 
or of ''mass selection" as it is now called. By this system, 
a selection of seed was made from a large number of plants 
and the whole thrown together and sown "en masse" 
in a single plot. But it soon became evident that this 
method of selection was not yielding the results which the 
Swedish farmers demanded — better varieties which would 
be constant. The method of selection was therefore 
changed and in two years the difficulties were being over- 
come by the new method. 

This new method consisted of testing individual plants 
and their progeny instead of making, at once, a com- 
posite test of many plants. This plan of individual 
selection has proved itself. The results were convincing. 
It left no doubt as to the fact that the only true starting- 
point for the fixation of different types must be plants 
taken one by one. 



308 Plant-Breeding 

This Swedish discovery has changed the outlook on 
the problem of plant-breeding, especially the methods of 
selection. It could be easily demonstrated that there 
existed in any cultural variety of plants a large number 
of independent forms having widely divergent quahties 
and a practical value that was quite useful. It was 
found, moreover, that most of the descendants or ''pedigree 
culture " of single individuals were constant. 

In employing the old method of ''mass selection," 
they were working bhndly without knowing how or when 
or even whether they were going to reach a stabiHty of 
type ; on the other hand the method of pedigreed culture 
or "individual selection" ehminated the fear of failure 
because of the appearance of the hitherto unsurmountable 
variations. The varieties are already there, and fixed 
from the beginning of the work ; the only difficulty is to 
learn to recognize them and to place the proper valuations 
upon them. 

The success of this method of breeding at Svalof has 
profoundly modified the method of selection in this 
country. The principle almost universally applied now 
is the method of individual selection. Thus we hear 
about plant-to-row, head-to-row, ear-to-row, or tuber-unit 
testing, depending upon the plant used. 

This method of selection is by no means the only one 
used for plant improvement at the Swedish station, hy- 
bridization also plays an important part in the work. 

The work has grown very rapidly and has now been 
split up into different departments with an expert in 
charge of each. 

Commercial breeding agencies. — The chief among com- 



The Forward Movement in Plant- Breeding 309 

mercial breeding agencies are, of course, the professional 
seedsmen. The demand for '^ novelties " is ever present 
and the seedsman must meet it. Therefore every seeds- 
man's catalogue each spring features them, giving them 
a prominent place and often painted in radiant colors. 
Everybody knows that novelties are often no better 
than the old standard sorts. But this demand for some- 
thing new seems to be inherent. 

It does not seem to be the common practice among 
American seedsmen to produce their own novelties by 
precise and recognized plant-breeding methods. Many 
of them are purchased abroad and others are accidental 
discoveries picked up here and there. 

Our standard sorts of seeds of all kinds are being 
gradually improved, but usually not by any particular up- 
to-date methods, except in certain unusual or exceptional 
instances. The seedsmen, however, carefully rogue their 
fields to eliminate divergent plants in an attempt to pro- 
duce seed of more importance. 

Recently, however, the American Seed Trade Associa- 
tion, consisting of the better class of seedsmen of the 
United States, has begun a general movement for im- 
proving crops by methods such as are used by careful 
breeders at the agricultural experiment stations. A 
committee on crop improvement has been organized 
whose duties are to ascertain, so far as possible, how the 
seed trade can be most helpful in these movements for 
better bred seed, and to bring about a close harmony 
between the seedsmen and the plant-breeding experts of 
the agricultural experiment stations. 

Many seedsmen feel, at present, that the extra cost 



310 Plant-Breeding 

entailed in producing pedigreed seed will not be ade- 
quately paid for by the average American buyer. There 
is probably much justification for this feeling. Two 
things should be done — to educate the buying public to the 
importance of better seed and the justification for its 
greater cost, and also to devise methods whereby this 
seed may be more cheaply and economically produced. 
The agricultural colleges through various channels are 
doing much to solve these two difficulties. 

Work of the council of grain exchanges. — The National 
Council of Grain Exchanges is the associated body of the 
various grain exchanges or boards of trade of this coun- 
try. This organization is interested in a larger yield of 
better grain. It has a crop improvement committee 
which is very active in grain-improvement work, including 
grain-breeding. This committee is conducting a very 
extensive publicity campaign in an attempt to induce 
farmers to use select seed and improve their crops. The 
executive work is done by a secretary, who acts as general 
manager, and an agronomist, who is an expert plant- 
breeder and advises concerning the technical features of 
the work, most of which is done through the county 
agents. To aid in this work, the , committee publishes a 
monthly publication called The County Agent, a paper 
filled with terse information concerning all phases of farm 
improvement work. The secretary and agronomist have 
large funds at their disposal, which are being used to bring 
about concerted action by farming communities for the 
improvement of seed grain. 

United States Department of Agriculture and state experi- 
ment stations, — The most methodical plant-breeding is 



The Forward Movement in Plant-Breeding 311 

now being clone by officers of the experiment stations in 
the United States and Canada, and by the United States 
Department of Agriculture. In most of the experiment 
stations there is at least one person interested in improv- 
ing horticultural plants and others interested in field 
crops ; as there is an experiment station in every state 
and territory and in the provinces of Canada, it will be 
seen that there are several hundred persons who, by 
their profession, are directly concerned in plant-breeding, 
aside from a number of persons in the federal Department 
of Agriculture who devote themselves exclusively to this 
subject. The work is extended, also, into the hands of 
various assistants in the different institutions ; so that it 
is probably no exaggeration to say that three to four 
hundred professional investigators are now giving atten- 
tion, for a greater or less part of their time, to measures 
for improving American crop production by means of 
breeding. 

The breeding enterprises of the federal Department of 
Agriculture were formerly confined to investigators in the 
Plant-Breeding Laboratory. But the work has grown to 
such an extent and breeding now touches so many phases 
of plant work that the former organization, as such, has 
been discontinued, and breeding is taken up in connec- 
tion with many other departments. There is now more 
of a tendency for the administrative divisions to group 
themselves around the crops such as corn, cotton, wheat, 
vegetables, and so forth, rather than processes such as 
plant-bre.eding, or culture. 

The work of the federal investigators has been tre- 
mendously important both from the standpoint of original 



312 Plant-Breeding 

research and the production of improved varieties and 
strains for dissemination. 

The success of the cotton-breeding experiments is 
noteworthy. These have been conducted with the object 
of increasing the length and strength of lint ; and an early 
variety to avoid the ravages of the boll-weevil is desired. 
The famous long-stapled Sea Island Cotton has been 
much used for hybridizing with the upland cottons to 
increase the length of lint of the latter. The length has 
been increased very considerably by this method and the 
varieties have been made more uniform, an important 
factor in ginning. 

The work of Webber and Swingle in producing new 
types of oranges which are resistant to cold is exceedingly 
important. Various varieties of the common sweet 
orange were crossed with Poncirus (or Citrus) trifoliata, a 
hardy hedge orange, and hybrids have been produced which 
are called " citranges." These will grow some four hundred 
miles farther north than the present orange belt, which is 
no small factor in orange-growing. These hybrids are too 
bitter to be eaten out-of-hand, but they make an excellent 
ade ; many of them have more juice than lemons. 

A cross has also been made between the pomelo or 
grapefruit and the tangerine. A hybrid was produced 
which combines the easily removable rind of the tan- 
gerine and has the flavor, not of the pomelo, but of the 
sweet orange. A fruit of this kind, combining these char- 
acteristics so well, bids fair to play an important part in 
orange-growing of the future. 

The division of Plant Introduction has contributed no 
small part to breeding work. Through its activities, a great 



The Forward Movement in Plant-Breeding 313 

many plants have been imported from all over the world 
which have formed rich material for the plant-breeder to 
take and improve, and many other varieties have been 
introduced which have immediately become valuable 
without further improvement. Such plants as durum 
wheat, Japanese kinshu rice, Swedish select oats. Wash- 
ington nave] orange, cold-resistant varieties of alfalfa, 
Russian apples, varieties of dates for Southern Cali- 
fornia and Arizona, drought-resistant olives, Egyptian 
cotton, and very many others have added millions to our 
agricultural wealth. 

The work of Orton and his associates in breeding plants 
resistant to disease forms an important chapter in this 
work. They have been successful in Avaging war on wilt 
of cotton, cowpeas, watermelons (see Figs. 55 and 56), and 
other crops by means of breeding to obtain wilt-resistant 
strains. The only successful method of combating certain 
maladies seems to be in this way. Strains of disease-resist- 
ant asparagus and of rust-resistant cereals have reached 
economic importance. 

Many great sections of the United States which are 
now nearly barren could be made productive if varieties 
of plants could be developed which are resistant to drought 
and alkali. This work has occupied the attention of a 
large corps of plant-breeders and not without results. 
The experts from eighteen state experiment stations be- 
sides the men from Washington are engaged in this work. 
As a result, varieties of wheat and other cereals, alfalfa, 
nuts, olives, and various fruits have been developed which 
will grow in parts of this great region and are of considerable 
economic importance. 



314 Plant-Breeding 

Work of the state agricultural experiment stations. — 
Investigators in the state experiment stations have always 
taken an active part in plant-breeding work. Five years 
ago, in an admirable editorial in the Experiment Station 
Record, Dr. Allen says as follows: "The list of proj- 
ects conducted by the experiment stations under the 
Adams fund includes sixty-three which fall under the head 
of investigations in breeding (eleven of these relate to the 
breeding of animals). This relatively large number indi- 
cates the popularity of the subject, and an evident feeling 
that it not only presents large research possibility, but is 
a line in which investigation is greatly needed. The 
attention which is being given to breeding is encouraging 
and the number of enterprises suggests the possibility of 
material additions to the general understanding of its 
various phases." 

The experiments subsequent to that time have, to a 
considerable extent, justified the hope of '^ material 
additions to the general understanding of its various 
phases." Numerous bulletins have been published which 
have added to that knowledge, and the experiment station 
men have written many articles which have appeared in 
various serial publications. 

The lines of work which have received the greatest 
attention and in which the most constructive work has 
been done are the application of Mendel's laws to economic 
plants and the elucidation of individual selection and pure- 
line breeding. Not only have important practical results 
been obtained in improving our economic plants, but a 
considerable amount of material of scientific value has 
been accumulated. 



The Forward Movement in Plant- Breeding 315 

The experiments with corn at the IlHnois and other 
experiment stations and those with timothy at the Cornell 
station stand out prominently as examples of pieces of 
scientific research which, at the same time, have tre- 
mendous economic importance. 

There is scarcely an economic crop but is receiving 
some attention by the plant-breeders of our experiment 
stations, and bulletins are appearing frequently dealing 
with this phase of the work. 

Many experiment stations, such as Wisconsin, Minne- 
sota, Ohio, New York, and Kansas, are also busily engaged 
in producing superior varieties upon their own grounds 
for distribution to their constituents. 

The old-time very prevalent variety tests are still 
made, but these are now supplemented by variety im- 
provement and careful studies of variety adaptation. 

Beside the large amount of practical work which most 
of the stations are doing, there are a large number of 
breeding projects prosecuted by them, and which are 
destined to become of scientific importance. 

The following projects have been reported by Dr. 
Allen of the federal Office of Experiment Stations as 
now conducted at the different stations : — 

Breeding Corn — Alabama Station. 

Breeding Experiments with Cotton — Alabama Station. 
Breeding Oats — Alabama Station. 
Wheat Breeding Investigations — Kansas Station. 
Alfalfa Breeding Investigations — Kansas Station. 
Analysis of Cellular Structure of Hybrids — Maine Station. 
Experimental Modification of the Hereditary Process — Maine 
Station. 



316 Plant-Breeding 

Breeding Alfalfa with Reference to the Extreme and Sub-tropical 

Conditions of Arizona — Arizona Station. 
Cotton Breeding — Arkansas Station. 
Nicotiana Hybrids — California Station. 
Improvement of Dent, Flint, and Sweet Corn in Yield and 

Feeding Value, by Breeding Work in Six Different Localities 

— Connecticut Station (State). 
Breeding Investigations with Tobacco — Connecticut State 

Station. 
Zenia in Maize and Hereditary Transmission of Various Char- 
acters — Connecticut State Station. 
The Effect of Variations in Physical Characters and Chemical 

Composition of the Corn Kernel upon the Vigor of the 

Plant — Delaware Station. 
Plant Breeding — Florida Station. 
Investigation of Mendelian Laws in Application to the Cotton 

Plant — Georgia Station. 
Inheritance of Contrasted Characters — Mississippi Station. 
Study of the Correlation of Characters and of Inheritance in 

Pure Lines and Varieties — Montana Station. 
Degree of Close Breeding in Maize — Nebraska Station. 
Plant Breeding Work with Pure Lines of Cereals — New Mexico 

Station. 
Place Variation with Cotton — North Carolina Station. 
The Increase and Fixation of Desirable Properties in Plants — 

Ohio Station. 
Breeding Drought-resistant Corn ; Study of Qualities of Drought 

Resistance — Oklahoma Station. 
Breeding Sorghums, especially Kafir Corn, Milo Maize, and 

Broom Corn, to secure more Drought-resistant Types — 

Oklahoma Station. 
Fundamental Study of Inheritance in Cotton — Texas Station. 
Comparative Studj^ of Durum, Poulard, and Bread Wheats — 

Arizona Station. 



The Forward Movement in Plant- Breeding 317 

Study of Principles Underlying the Development of Disease 

Resistance or Immunity in Farm Crops — North Dakota 

Station. 
Effects of Pollen from Barren Stalks of Corn — South Carolina 

Station. 
Breeding a Strain of Peaches resistant to Brown Rot — Alabama 

Station. 
Biological Analysis of Papago Sweet Corn for the Synthesis of 

Desirable Characters — Arizona Station. 
Principles relating to Transmission of Characters in the 

Apple as affected by Selection and by Crossing — Illinois 

Station. 
Apple Breeding — Iowa Station. 

Investigations upon Asparagus — Massachusetts Station. 
Study of the Principles of Heredity underlying Disease and 

Climatic Resistance in the Apple, Plum, and Strawberry — 

Minnesota Station. 
Heredity in Plants — Nebraska Station. 
Studies of Heredity in Vegetables, especially Squashes and 

Tomatoes — New Hampshire Station. 
Carnation Breeding — New Hampshire Station. 
Nature of the Inheritance and Correlation of Structural Char- 
acters in Crosses — New Jersey Station. 
Improvement of Mexican Chili by Breeding and Selection — 

New Mexico Station. 
Investigation of the Laws of Inheritance in Hybridization — 

New York (Cornell) Station. 
An Investigation of Mutation and Other Types of Variation 

in Wild and Cultivated Plants, to determine their Value 

in Plant Breeding — New York (Cornell) Station. 
Influence of Environment in producing Variation of Value to 

the Breeder — New York (Cornell) Station. 
Study of Transmission of Characters in Hybrids of Rotundifolia 

Grapes — North Carolina Station. 



318 Plant- Breeding 

A Study of the Fecundation of the Rotundifolia Grapes — South 
Carolina Station. 

Improvement of Hardy Wild Fruits of the Northwest by Breed- 
ing and Crossing — South Dakota Station. 

The Breeding of Apple and Pear Varieties for Resistance to 
Blight — Tennessee Station. 

Breeding Work with Blackberry — Texas Station. 

Breeding Experiments with Apples — Virginia Station. 

Mendelism of the Hybrids of Blackberries and Raspberries, 
particularly with Reference to Leaf Structure and Habits 
of Growth — Washington Station. 

Pollination of the Apple — West Virginia Station. 

Investigation of Mendel's Law as applied to Hybridizing the 
White with the Black Varieties of Muscadine Grape — 
Georgia Station. 

Apple Breeding Investigations — Idaho Station. 

Effects of Fertilizers on Cell Structure of Crops and their Rela- 
tions to Mutations in Fruits, Vegetables, and Flowers — 
Maryland Station. 

Investigations on "Double Flower" and Sterility in Blackberries 
and Dewberries — North Carolina Station. 

Pollination of the Apple and Conditions affecting It — Oregon 
Station. 

In addition to the work of the experiment station men, 
very much highly valuable work is under way by such 
men as East at Harvard, Shull at Cold Spring Harbor, 
Harper and Stout at the New York Botanical Garden, 
Bradley Moore Davis at the University of Pennsylvania, 
B. M. Duggar at the Missouri Botanical Garden, and many 
others. This research is undertaken by well-trained 
specialists who are producing the very highest type of 
fundamental constructive results. 



The Forward Movement in Plant- Breeding 319 




320 



Plant-Breeding 




The Forward Movement in Plant- Breeding 321 

Instruction in plant-breeding in the United States. — One 
of the most, if not the most, significant advances that 
plant-breeding has made in recent years is the increase in 
the amount of instruction given in the agricultural colleges 
and other agricultural schools. 

Formerly, the only teaching of this subject was in 
connection with a course of horticulture, probably, 
and the breeding was likely to receive minor considera- 
tion. 

All of this has been changed. Strong courses are 
given in this subject in all of the agricultural colleges. 
Some go so far as to have separate departments or divi- 
sions in which the staff devotes all of its time to plant- 
breeding instruction and investigations. It is estimated 
that over two thousand students receive regular plant- 
breeding instruction each year in this country. This is 
bound to have tremendous influence upon practical 
plant improvement on the farms of the country. Plant- 
breeding holds a very prominent place in the instruction 
given to short-term students, as it should, and in the 
form of various extension enterprises. 

Luther Burhank. — In addition to the large number of 
plant-breeders who have some official connection with 
the state experiment stations or the federal government, 
there has always been a number of men who have 
maintained private plant-breeding establishments. Chief 
among these is Luther Burbank. He will always be given 
a prominent place in American horticulture because of the 
many and valuable varieties which he has added to it. 

The practical results, however, that Mr. Burbank has 
secured have been praised by the writers beyond reason. 



322 



Plant-Breeding 




a 






03 



'a 

CO 



CO 

o 






The Forward Movement in Plant-Breeding 323 

His place abounds in interesting and surprising things, 
just as would be expected of any man's place if conducted 
under similar conditions (Figs. 101-103), and many of the 
things will undoubtedly have great value. His work has 
been so much written about that it is not necessary to 
make any catalogue of the things that are under his hand. 
It is not too much to hope that some of his productions, 
as the plumcots, may be the starting-points of strong and 
noble lines of evolution. Some of those that have been 
much heralded are of doubtful economic value. 

The value of Mr. Burbank's work lies above all merely 
economic considerations. He is a master worker in mak- 
ing plants to vary. Plants are plastic material in his 
hands. He is demonstrating what can be done. He is 
setting new ideals and novel problems. Heretofore, 
gardeners and other horticulturists have grown plants 
because they are useful or beautiful : Mr. Burbank grows 
them because he can make them take on new forms. 
This is a new kind of pleasure to be got from gardening, 
a new and captivating purpose in plant growing. It is a 
new reason for associating with plants. 



APPENDIX A 

GLOSSARY OF TECHNICAL PLANT-BREEDING 

TERMS 

Allelomorph. — One of the pure unit-characters commonly 
existing singly or in pairs in the germ-cells of mendelian hybrids, 
and exhibited in varying proportion among the organisms them- 
selves. Thus an allelomorphic pair of characters comprises the 
opposed units, one of which comes from each parent in a hybrid. 
For example, the roundness and wrinkledness found in two varie- 
ties of peas is an allelomorphic pair. 

Biometry. — The application of statistical methods to biological 
problems. 

Chromosome. — A term applied to certain minute bodies, in 
the nuclei of the animal and vegetable cells which appear at 
definite periods in the division of the cell ; they are constant in 
number for each species of animal or plant, and are characterized 
by the fact that they stain very deeply with certain dyes. The 
chromosomes are supposed to be the bearers of heredity. 

Dominant characters. — It often occurs, when* two varieties 
or species are crossed, that the characters of one appear in the 
first generation hybrid to the exclusion of the other. These 
are called dominant characters. 

Duplex. — The state of inheriting a character that is present 
in both parents. 

Epistatic. — Used to describe a color factor which, in hybrid- 
ization, covers up or hides other color factors in the first genera- 
tion hybrid (opposed to hypostatic). 

325 



326 Plant-Breeding 

Factor hypothesis. — An assumption that organisms may 
contain various hereditary units which do not appear in their 
body cells. This is especially applied to color units. Very 
often these factors do not appear until the plant has been crossed 
with another plant containing a complementary factor. 

Fi. — A symbol introduced by Bateson, to designate the 
first filial or hybrid generation. 

F2. — A symbol for the second generation. 

/^3. — A symbol for the third hybrid generation. And so on. 

Galton curve. — A curve, devised by Galton, when the values 
for all the individuals are recorded consecutively in an ascending 
series. The class values are plotted on the vertical axis. 

Gamete. — A mature sex- or germ-cell , which will produce a 
new individual upon uniting with another such cell of the op- 
posite sex. 

Genetics. — A study of the phenomena of variability and 
heredity, or of the physiology of descent, as affecting individuals 
or races of plants, animals, or human beings. 

Genotype. — A type represented by individuals of the same 
germinal constitution. The nature of such a type can be 
determined only by a breeding test, not by inspection. 

Heterozygote. — An individual formed by the union of two 
germ-cells of unlike constitution. 

Homozygote. — An individual which is of a pure type in regard 
to a certain character because both of its parents were of the 
same gametic constitution. 

Hybrids. — The offspring of crosses between individuals of 
distinctly different natures. 

Hypostatic. — Used to describe a color factor which is con- 
cealed by higher color factors. (See Epistatic.) 

Mutation. — A sudden variation, differing from its parents 
in a distinct character or characters, and able to transmit its 
new characters in full degree to its offspring. 

Nulliplex. — A condition of an individual when it does not 



Appendix A 327 

possess a character because neither of its parents carried the 
possibilities for such a character in their germ-cells. 

Phenotype. — The visible type of a group as expressed by 
external characteristics. Opposed to genotype. There may be 
several genotypes in a phenotype. 

Plateation. — (From the Latin platea, meaning place.) A 
physiological variation caused by external influences such as 
locality, climate, soil, and so forth; sometimes called place- 
variation. It IS what Darwin called " definite variation." This 
word was coined to express in one word the third of the three 
kinds of variation — fluctuation, mutation and plateation . (Here 
first defined.— A. W.G.) 

Qiietelet curve. — A curve which shows the relative frequency 
with which individuals of a given lot, or population, occur in 
certain classes. Class values are plotted on the horizontal 
line and frequencies on the vertical. The mode is the highest 
point of such a curve and represents the dominating type of 
the character studied. 

Recessive characters. — (See Dominant characters.) The 
characters which are entirely covered up the first generation 
but reappear the second and subsequent generations. 

Segregation. — The reappearance in definite ratios, in the 
second hybrid generation, of the characters of two forms crossed ; 
and the first hybrid generation (when this differs from the 
dominant character). 

Simplex. — The condition of an individual which has inherited 
a character from only one parent. 

Somatic. — Of, or pertaining to, the body as opposed to the 
germ-cells. 

Xenia. — The results of a cross-fertilization between different 
varieties of plants due to a double fertilization; found in such 
plants a^ corn, peas, etc. 

Zygote. — The result of the union of two gametes. (See 
Gamete.) 



APPENDIX B 

PLANT-BREEDING BOOKS 

Following is a brief list of books containing material more or 
less related to plant-breeding. This list is not intended to be 
complete, but is designed to give the reader an idea of the more 
important books on the subject. There are many books which 
are not listed upon the general subject of botany, others upon 
Heredity and evolution in their broadest phases, and still others 
upon animal breeding which will contain much material which 
is related to the subject of plant improvement by breeding. 

American Breeder's Association Reports. Washington, D.C. 

1905-1912. 
Bailey, L. H., Cyclopedia of American Agriculture. Vol. II, 

Crops. Macmillan Co. 1907. 
Bailey, L. H., Standard Cyclopedia of Horticulture. 6 vols. 

(Continuing) Alacmillan Co. 1914. 
Bailey, L. H., Sketch of Evolution of Our Native Fruits. xiii + 

472 pp., 125 figs. Macmillan Co. 3d edition. 1898. 
Bailey, L. }i.,The Survival of the Unlike. 515 pp., illus. Mac- 
millan Co. 1897. 
Bateson, W., MendeVs Principles of Heredity, xiv + 396 pp., 

9 pis., and 35 figs. Cambridge. 1909. 
Baur, Dr. Erwin, Einfuhrung in die experimentelle Vererbungs- 

lehre. 293 pp., 80 figs. Berlin. Gebriider Borntraeger. 

1911. 

328 



Appendix B 329 

Castle, W. E., Coulter, J. M., Davenport, C. B., East, 
E. M., Tower, W. L., Heredity and Eugenics. 315 pp., 
98 figs. The Univ. of Chicago Press. 1912. 

Castle, W. E., Heredity, in Relation to Evolution and Animal 
Breeding. 184 pp. N. Y. and London. D. Appleton Co. 
1911. 

Crampton, Henry Edw., The Doctrine of Evolution; its Basis 
and its Scope, ix +311 pp. N. Y, Columbia Univ. 
Press. 1911. 

Darbishire, a. D., Breeding and the Mendelian Discovery. 
xii + 282 pp. Cassell & Co. London. 4 colored pis., 
34 figs. 1911. 

Davenport, E., Domesticated Animals and Plants, xiv + 
312 pp., 49 figs. Ginn & Co. 1910. 

Davenport, E., and Rietz, H. L., Principles of Breeding (by 
E. Davenport). Appendix: Statistical Methods (by 
H. L. Rietz). A treatise on thremmatology, or the prin- 
ciples and practices involved in the economic improvement 
of domesticated animals and plants, xiii + 727 pp. 
Ginn & Co. Boston. 1907. 

Fifty Years of Darwinism, v + 274 pp., 5 pis., 1 fig. N. Y. 
1909. 

Fruwirth, C, et al.. Die ZUchtimg der LandwirtschaftUchen 
Kulturpflanzen. Vols. 1-5. 1904-1912. 

JoHANNSEN, W., Elcniente der E.vakten Erblichkeitslehre. vi + 
515 pp., 30 figs. Gustav Fischer. Jena. 1903. 

JoiL\NNSEN, W., Ueber Erblichkeit in Populationen und in reinen 
Linien. 68 pp., 8 figs. Gustav Fischer. Jena. 1903. 

Kellogg, V. L., Darwinism To-Day. 403 pp. Henry Holt 
& Co. N. Y. 1907. 

Knuth, p., Handbook of Flower Pollination. Vol. I, xix + 
382 pp. Oxford. Porter. 1906. 

Lang, H., Theorie und Praxis der Pflanzenzuchtung. viii + 
169 pp., 47 figs. 1910. 



330 Plant-Breeding 

LoBNER, M., Leitfaden fiir Gdrtnerische Pflanzenzuchtung. 

vii + 160 pp., 10 figs. Jena. 1909. 
Lock, R. H., Recent Progress in the Study of Variation, Heredity, 

and Evolution. 2d ed., xiv + 334 pp. Murray. London. 

4 pis., 45 figs., and 5 portraits. 1909. 

Newman, L. H., Plant Breeding in Scandinavia. 193 pp., 
63 figs. The Canadian Seed Growers' Association. Ottawa. 
1912. 

PuNNETT, R. C, Mendelism. 192 pp. N. Y. Macmillan Co. 

5 pis., 35 figs. 1911. 

Reid, G. a., The Laws of Heredity. 548 pp. Methuen & Co. 

London. 1910. 
RuMKER, VON K., Ueber Organisation der PfianzenzUchtung. 

56 pp. Berlin. 1909. 
Seward, A. C. (Editor), Darwin and Modern Science, xvii + 

595 pp., fig. and pi. 1909. 
Stevens, W. C, Plant Anatomy from the Standpoint of the 

Development and Functions of the Tissues and Handbook of 

Micro-technic. xii + 349pp. Blakiston's Son & Co. Phila- 
delphia. 136 illus. 1907. 
Thomson, J. Arthur, Heredity, xvi + 605 pp., 49 figs. 2d 

ed. 1912. 
Vernon, H. M., Variation in Animals and Plants, pp. ix + 

415, 30 figs. Henry Holt & Co. 1902. 
Vries, Hugo de. Species and Varieties, their Origin by Mutation. 

Edited by Daniel Trembly MacDougal. The Open Court 

Pub. Co. Chicago. 1904. 
Vries, Hugo de, Plant Breeding. Comments on the experiments 

of Nilsson and Burbank. xiii + 360, figs. 114. 1907. 
Vries, Hugo de. The Mtdation Theory. Vol. I, ''The Origin 

of Species by Mutation." Engfish translation by Prof. 

J. B. Farmer and A. D. Darbishire. xvi + 582 pp. The 

Open Court Publishing Co. Chicago. 4 pis. and 119 figs. 

1909. 



Appendix B 331 

Vries, Hugo de, The Mutation Theory. Vol. II, ''The Origin of 
Varieties by Mutation." English translation by Prof. 
J.B.FarmerandA.D.Darbishire. viii+ 683 pp. Chicago. 
The Open Court Publishing Co. 6 pis., 149 figs. 1911. 

Walter, Herbert Eugene, Genetics. An Introduction to the 
Study of Heredity, xiv + 264 pp. The Macmillan Co. 
N. Y. 72 figs, and Diagr. 1913. 

Wilson, E. B., The Cell in Development and Inheritance, xxi + 
483 pp., 194 figs. Macmillan Co. 1900. 

Yearbooks U. S. Department of Agriculture. 1894-1913. 

Hybrid Conference Report (First International Conference). 
London. Printed in Journal of the Royal Hort. Soc, April, 
1900. 

International Conference (Second) on Plant Breeding and Hybrid- 
ization. Proceedings published as Memoir, Vol. I. Hort. 
Soc. of New York. 1902. 

International Conference {Third) on Genetics. London. Report 
issued by Royal Hort. Soc. 1906. 

International Conference {Fourth) on Genetics. Report pub- 
lished in Paris, 1911, under Editorship of Ph. de Vilmorm. 



APPENDIX C 

LIST OF PERIODICALS CONTAINING BREEDING 

LITERATURE 

We have attempted to include in this list such periodicals 
as are most likely to contain breeding articles that may be of 
interest to the general reader and the teacher and student of 
Genetics. This list is not intended to be complete, but to in- 
clude the principal publications. 

Abbreviations : semi-a = semi-annual ; q = quarterly ; semi-q = semi- 
quarterly ; m = monthly ; bi-m = bi-monthly ; semi-m = semi-monthly ; 
w = weekly : semi-w = semi-weekly ; i = irregular. 

American Naturalist. New York. m. 

American Philosophical Society. Proceedings. Philadelphia. 
3 nos. 

Annales de la science agronomique. Paris, m. 

Annales des science naturelles. Botanique. Paris. 

Annals of Applied Biology. London. 

Annals of Botany. London, q. 

Archiv fiir Rassen- und Gesellschafts-Biologie. Leipzig, bi-m. 

Archives des sciences biologiques. St. Petersbourg. 

Association internationale des botanistes. Progressus rei 
botanicae. Jena, semi-a. 

Biological Bulletin, m. Wood's Hole, Mass. Marine Bio- 
logical Laboratory. 

Biologisches Centralblatt. Erlangen, Leipzig, semi-m. 

Biometrika. Cambridge, Eng. i. 

332 



Appendix C 333 

Botanical Gazette. Chicago, m. 

Botanische Zeitung. Abt. 1 and 2. Leipzig, w. 

Botanisches Centralblatt. Jena. w. 

Botanisches Centralblatt-Beihefte., Abt. 1 ; 3 nos. Anatomic, 

Histologic und Physiologic der Pflanzen. Abt. 2; 3 nos. 

Systcmatik, Pflanzengeographic, Augewandte, Botanik, etc. 

Dresden. 
Deutsche Botanische Gesellschaft. Berichte. Berlin, m. 
Deutsche Landwirtschafts-Gesellschaft. Jahrbuch. Berlin, q. 
Die Landwirtschaftlichen Versuch-Stationen. Berlin, semi-m. 
Florists' Exchange. New York. w. 

France — Institut national agronomique. Annales. Paris, i. 
Gardeners' Chronicle. London, w. 
Jahrbucher fur Wissenschaftliche Botanik (Pringsheini's). 12 

nos. Leipzig. 
Journal of Agricultural Research, m. 
Journal of Agricultural Science. Eng. q. 
Journal de botanique. Paris, m. 
Journal of Genetics. Cambridge, Eng. q. 
Journal of Heredity. Washington, m. 
La Cellule. Lierre. i. 
La Science agronomique. Paris. 
Linnean Society : 
Journal, botany. London, m. 
Transactions, botany. London, i. 
(The) Mendel Journal. London. 
New Phytologist. London. 10 nos. 
Physiological Researches. Baltimore, i. 
Plant World. Tucson, Ariz. m. 
Popular Science Monthly. New York. m. 
Quarterly Journal of Microscopical Science. London, q. 
Revue, generale agronomique. Uccle lez-Bruxelles. m. 
Revue generale de botanique. Paris, m. 
Royal Microscopical Society. Journal, bi-m. 



334 Plant-Breeding 

Royal Society of London, Philosophical transactions. 1. 

Science. New York. w. 

Society de biologie, Comptes rendus. Paris, w. 

Societe botanique de France. Bulletin. Paris, m. 

Societe des agriculteurs de France. Bulletin. Paris, semi-m. 

Society royale de botanique de Belgique. Bulletin. Bruxelles. 

Torrey Botanical Club. Bulletin. New York. m. 

United States Dept. of Agriculture, Office of Experiment 

Stations. Experiment Station Record. Washington. 16 

nos. 
Zeitschrift fiir Planzenziichtung. Wien. 
Zentralblatt fiir AUgemeine und Experimentelle Biologie. Leipzig. 



APPENDIX D 
BIBLIOGRAPHY 

Following is a list of miscellaneous references to writings on 
subjects related to plant-breeding. It is not intended to be 
either complete or comprehensive. This bibliography begins 
with the year 1905. References to -earlier writings may be 
found in the fourth edition of this work. 

For reference to the literature of cross-fertilization, the reader 
is directed to d'Arcy Thompson's list in Mueller's '' Fertiliza- 
tion of Flowers," and an extensive bibliography to the rapidly 
growing literature upon the heredity of color can be found in a 
technical bulletin by the junior writer of this book. This bulle- 
tin will soon be published by the Agricultural Experiment 
Station of Cornell University. 

1905. Balls, W. L., The Sexuality of Cotton. Khed. Agr. 
Soc. Yearbook, 199-222. 

1905. BiFFEN, R. H., Mender s Laws of Inheritance and Wheat 
Breeding. Jour. Agr. Sci., Cambridge, 1 : 4-48, 1 pi. 

1905. BiFFEN, R. H., The Inheritance of Sterility in the Bar- 
leys {Hordeum sativum, etc.). Jour. Agr. Sci. 1 : 250-257, 
Ifig. 

1905. Butler, E. J., The Bearing of Mendelism on the Suscep- 
tibility of Wheat to Rust. Jour. Agr. Sci. 1 : 361-363. 

1905. CoNKLiN, Edwin G., The Mutation Theory from the Stand- 
point of Cytology. Science, n.s. 21 : 525-529. 

1905. Eastman, C. R., On the Spelling of " Clon." Science, 
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335 



336 Plant-Breeding 

1905. Hurst, C. C, Notes on the " Proceedings of the Inter- 
national Conference on Plant Breeding and Hybridisation, 

1902r Roy. Hort. Soc. Jour. 29 : 417-433. 
1905. Jones, L. R., Disease Resistance of Potatoes. U. S. 

Dept. Agr. Bur. Plant Ind. Bull. 87 : (39 pp.). 
1905. Jones, L. R., Concerning Disease Resistance of Potatoes. 

Vermont Agr. Exp. Sta. 18 : 264-267. 
1905. Klinck, L. S., Corn Breeding in the Corn Belt. Can. 

Seed-Grow. Assoc. Rep. 2: 56-61. 
1905. Pearl, Raymond, Investigation by Statistical Methods of 

Correlation in Variation. Carnegie Inst. (Wash., D.C.), 

Yearbook (1905) (No. 4) : 285-286. 
1905. Pearl, Raymond, Note on Variation in the Ray Flowers 

of Rudheckia. Am. Nat. 39 : 87-88. 1 fig. 
1905. Petrunkevitch, Alexander, Natural and Artificial 

Parthenogenesis. Am. Nat. 39 : 65-76. Bibliog. 
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Science, n.s. 22 : 87-88. 
1905. Pollard, Charles Louis, " Clon " versus " Clone.'' 

Science, n.s. 22 : 463. 
1905. Shamel, a. D., The Effect of Inbreeding in Plants. U. S. 

Dept. Agr. Yearbook, 377-392. 3 pis., 1 fig. 
1905. Shamel, A. D., Tobacco Breeding Experiments in Conn. 

Conn. (State) Agr. Exp. Sta. Ann. Rep. 331-343. 
1905. Starnes, Hugh N., Japan and Hybrid Plums. Georgia 

Agr. Exp. Sta. 68 (see pp. 1-40). 
1905. Vries, H. de, Dauer der Mutationsperiode bei CEnothera 

Lamarckiana. Deutsch. Bot. Gesell. Ber. 23 : 382-387. 
1905. Vries, H. de. The Mutation Theory. Gard. Chron. 

3d ser. 37 : 321-322. 
1905. Webber, Herbert J., The Science of Plant Breeding. 

Can. Seed-Grow. Assoc. Rep. 2 : 79-92. PL II., fig. 1 & 2. 
1905. Webber, Herbert J., Pedigree or Grade Breeding. Can. 

Seed-Grow. Assoc. Rep. 2 : 61-70. PL, Photo., Fig. 



Appendix D 337 

1905. WiESNER, J., Untersuchungen uber den Lichtgenuss der 
Pflanzen im Yellowstone Gebiete und in anderen Gegenden 
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1905. Williams, C. G., Pedigreed Seed Corn. Ohio Agr. Exp. 
Sta., Circ. 42: 1-11. 

1906. Andrews, F. M., Some Monstrosities in Trillium. Ind. 
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1906. Bateson, W., and Saunders, Miss E. R., and Pun- 
nett, R. C, Inheritance in Sweet Peas and Stocks. Roy. 
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1906. Bateson, W., Coloured Tendrils of Sweet Peas. Gard. 
Chron. 39 : 333. 

1906. BeaL; W. J., Improving Wild Potatoes by Selection. Soc. 
Prom. Agr. Sci. Proc. 27 : 75. 

1906. BiFFEN, R. H., Experiments on the Hybridization of 
Barley. Phil. Soc. Proc. (Cambridge), 13:304-308. 

1906. Blanchard, W. H., A New Dwarf Blackberry. Torreya 
6 : 235-237. 

1906. Buchanan, J., Some Effects in Varieties of Cereal Crops 
arising from Different Conditions of Growth. Can. Seed- 
Grow. Assoc. Rep. 3 : 74-77. 

1906. Card, F. W., Blake, M. A., and Barnes, H. L., Rasp- 
berry Score Card. Rhode Island Agr. Exp. Sta. 168-169. 

1906. Card, Fred W., Apple Breeding. Rhode Island Agr. 
Exp. Sta. 20:250-252. 

1906. Card, Fred W., Corn Selection. Rhode Island Agr. 
Exp. Sta. Ann. Rept. 20 : 216-220. 

1906. Castle, W. E., hibreeding, Crossbreeding and Sterility 
in Drosophila. Science, n.s. 23 : 153. 

1906. Crocker, W., Role of Seed Coats in Delayed Germination. 
Bot. Gaz. 42:265-291. Fig. 



338 Plant-Breeding 

1906. DuvEL, J. W. T., The Germination of Seed Corn. U. S. 
Dept. Agr. Farmers' Bull. 253 : (16 pp.), 4 figs. (Includ- 
ing : Value of a germination test. Average yield of corn 
to the acre. Testing individual ears. Selecting seed ears. 
Numbering the ears. The germination box. Results of 
tests.) 

1906. Gager, C. S., De Vries and His Critics. Science, n.s. 
24 : 81-89. Bibliog. in notes. 

1906. Graenicher, S., Some Notes on the Pollination of Flowers. 
Wis. Nat. Hist. Soc. Bull. 4 : 12-21. 

1906. Griffon, E., Le greffage des Solanees. Acad. Sci. Compt. 
Rend. 143:1249-1251. 

1906. Haacke, Wilhelm, Die Gesetze der Rassenmischung 
und die Konstitution des Keimplasmes. Arch. f. Entwick'- 
mech. d. Org. 21 : 1-93. 104 tab. 

1906. Halsted, B. D., Breeding Sweet Corn — Cooperative 
Tests. New Jersey Agr. Exp. Sta. Bull. 192 : 1-30. Fig. 

1906. Heckel, E., Variation in the Potato Tuber. Gard. 
Chron. 3d ser. 39 : 88. 

1906. Henslow, G., Evolution and Adaptation. Roy. Hort. 
Soc. Jour. n.s. 31 : 159-163. 

1906. Henslow, G., The True Meaning of " Natural Selec- 
tion " and the "Survival of the Fittest " in Nature. Roy. 
Hort. Soc. Jour. n.s. 31 : 90-96. 

1906. Henslow, G., Species and Varieties; their Origin by 
Mutation. Roy. Hort. Soc. Jour. n.s. 31 : 164-168. 

1906. Hesketh, R. T., Apple Grafted on Hawthorn. Gard. 
Chron. 3d ser. 39 : 347. 

1906. Hurst, C. C., Mendelian Laws of Inheritance. Gard. 
Chron. 3d ser. 39: 187. 

1906. Le Clerc, J. A., The Effect of Climatic Conditions on the 
Composition of Durum Wheat. U. S. Dept. Agr. Year- 
book: 199-212, 2 pis. Same. Yearbook Separate, 417: 
199-212, 2 pis. 



Appendix D 339 

1906. Lock, R. H., Plant Breeding in the Tropics. III. Ex- 
periments with Maize. Roy. Bot. Gard. Ann. 3:2: 95- 
184. 

1906. Macoun, W. T., The Improvement of the Potato. Can. 
Seed-Grow. Assoc. Rep. 3 : 77-84. Photo., Fig. 

1906. Morgan, T. H., Are the Germ-cells of Mendelian Hybrids 
"Pure "f Biol. Centralbl. 26 : 289-296. 

1906. MuNSON, W. M., Plant-breeding in its Relation to Ameri- 
can Pomology. Maine Agr. Exp. Sta. Bull. 132 : 149-176. 

1906. Ortmann, a. E., The Mutation Theory Again. Science, 
n.s. 24 : 314-317. Bibliog. in notes. 

1906. OsTERHOUT, W. J. v., Experiments with Plants, x + 
493 pp. TheMacmillanCo.,N.Y. 252 figs. Rev. in Am. 
Nat. 40 : 146-148. 

1906. Pearl, Raymond, Variation in the Number of Seeds of 
the Lotus. Am. Nat. 40 : 757-768. 4 figs. 5 tab. 

1906. Raunkiaer, C, Transmission par heredite dans les 
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1906. Riviere, G., and Bailhache, G., Influence du porte- 
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847. 

1906. Rosenberg, 0., Embryobildung in der Gattung Hieracium. 
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1906. Saame, 0., Kernverschnelzung bei der karyokinetischen 
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sacks von Fritillaria imperialis. Deutsch. Bot. Gesell. 
Ber. 24 : 300-303, 1 pi. 

1906. ScHARF, E., Keimkraft-Apparat. Deutsch. landw. 
Presse 33 : 507-508, 514^516. 

1906. Schulte, J. L, Corn Breeding Work at the Experiment 
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1906. Solms(-Laubach), H. Graf zu, Cruciferenstudien. 
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1 : 15-43, 1 pi. 



340 Plant-Breeding 

1906. Sperling, J., Korrelation zwischen Kornfarbe und Aehren- 

formen beim Roggen. Fiihlings landw. Zeitung, 55 : 93-99. 
1906. Stuart, W., Disease Resistance of Potatoes. Vermont 

Agr. Exp. Sta. Bull. 122: (see pp. 107-136). Abstr. in 

Exp. Sta. Rec. 17 : 1078. 
1906. Van den Heede, A., Variation chez les vegetaux. Soc. 

Nantaise d'hort. Ann. 79 : 97-103. 
1906. Vries, H. de, Aelters und neuere Selektionsmethode. 

Biol. Centralbl. 26 : 385-395. 
1906. Vries, H. de, Die Svalofer Methode zur Veredelung land- 

wirtschaftlicher Kulturgewdchse und ihre Bedeutung fur 

die Selektions-Theorie. Arch. Rassenbiol. 3 : 325-358, 
1906. Vries, H. de, Species and Varieties; their Origin by 

Mutation. Second edition, xviii + 847 pp. 
1906. Webber, H. J., New Citrus and Pineapple Productions 

of the Department of Agricidture. U. S. Dept. Agr. Year- 
book, 329-346. 8 pis., 1 fig. Same. Yearbook Separate, 

427:329-346. 8 pis., 1 fig. 
1906. Weismann, a.. The Evolution Theory. Translated with 

the author's cooperation by J. A. & Margaret R. Thomson. 

2 vols, xvi +416 pp. and 405 pp. E. Arnold. London. 

Rev. in Am. Nat. 40 : 375-377. 
1906. WiANCKO, A. T., Corn Improvement. Indiana (Purdue 

Univ.) Agr. Exp. Sta. Bull. 110:79-120. 14 figs. 
1906. WiLBRiNK, G., Deuxieme rapport sur les experiences de 

selection faites avec Vindigotier de Natal. (In Dutch.) 

Buitenzorg (1906), 1-20. 
1906. Wilson, E. B., Mendelian Inheritance and the Purity 

of the Gametes. Science, n.s. 23: 112-113. 
1906. Wilson, Edmund B., Studies on Chromosomes. III. The 

Sexual Differences of the Chromosome-groups in Hemiptera, 

with Some Considerations on the Determination and Heredity 

of Sex. Jour. Exp. Zool. 3: (No. 1). Rev. in Arch. f. 

Entwick'mech. d. Org. 21 : 357. 



Appendix D 341 

1906. Winkler, H., Morphologie und Biologie tropischer Bluten 

und Fruchte. Bot. Jahrb. 38 : 233-271. 
1906. Winkler, H., 'Parthenogenesis bei Wikstroemis indica 

(L.), C. A. Mey, und ihre Bedeutung filr die Lehre der Be- 

fruchtung. Jard. Bot. Ann. n.s. 5 : 208-276, 4 pis. 
1906. WiTTMACK, L., Berichte ilber die internationale Konferenz 

uber Hybridisation und Pfianzenzucht in London vom 30. 

Juli bis 3. August 1906. Gartenflora 55: 481-486, 509- 

511. 
1906. WiTTMACK, L. The Influence of the Graft on the Rooting 

of the Pear. Gard. Chron. 3d ser. 40 : 150. 

1906. WiTTMACK, L. Sports. Gard. Chron. 3d ser. 40 : 223. 

1907. Balls, W. R., Note on Mendelian Heredity in Cotton. 
Jour. Agr. Soc. 2 : 216. 

1907. Bessey, C. E., a Sijnopsis of the Plant Phyla. Univ. 
Studies, Univ. of Nebraska, 7 : 275-373. 1-99. 

1907. BiFFEN, R. H., Studies in the Inheritance of Disease Re- 
sistance. Jour. Agr. Sci. 2 : 109. 

1907. BiFFEN, R. H., The Hybridization of Barleys. Jour. 
Agr. Sci. 2 : 183. 

1907. BouLENGER, G. A., On the Variations of the Evening 
Primrose, (Enothera biennis. Jour. Bot. 45 : 353-363. 

1907. Brown, Arthur Erwin, Variation or Mutation. Science, 
n.s. 25 : 107-108. 

1907. Brownlee, John, Statistical Studies in Immunity. A 
discussion of the means of estimating the severity of cases of 
acute diseases. Biometrika, 5 : 423-435. Tab., Diagr. 

1907. Butler, E. J., The Selection of Sugarcane Cuttings. 
Agr. Jour. India, 2 : 193. 

1907. Card, Fred W., Cherry Crosses. Rhode Is. Agr. Exp. 
Sta. Rep. 258-259. 

1907. Castle, W. E., On a Case of Reversion Induced by Cross- 
breeding and its Fixation (guinea-pig). Science, n.s. 25: 
151-153. 



342 Plant-Breeding 

1907. CocKERELL, T. D. A., Is there Determinate Variation? 

Science, n.s. 25 : 34. 
1907. Cook, 0. F., Mendelism and Other Methods of Descent. 

Washington Acad. Sci. Proc. 9 : 189-240. 
1907. Crosthwait, G. A., Indian Corn. Its Production and 

Improvement. Idaho Agr. Exp. Sta. Bull. 57. 
1907. Davenport, C. B., Heredity and MendeVs Law. Wash- 
ington Acad. Sci. Proc. 9 : 179-187. 
1907. Davenport, E., and Rietz, H. L., Type and Variability 

in Com. Illinois Agr. Exp. Sta. Bull. 119 : 1-29. 
1907. Davidson, A., The Changes in our Weeds. So. Calif. 

Acad. Sci. Bull. 6:11-12. 
1907. East, E. M., The Relation of Certain Biological Principles 

to Plant Breeding. Connecticut Agr. Exp. Sta. Bull. 158 : 

1-93. Fig. 
1907. East, Edward M., Some Essential Points in Potato 

Breeding. Conn. (State) Agr. Exp. Sta. Ann. Rep. 429-448. 
1907. East, Edward M., Inbreeding in Corn. Conn. (State) 

Agr. Exp. Sta. Ann. Rep. 419-429. 
1907. East, Edward M., Better Seed Corn in Conn. Conn. 

(State) Agr. Exp. Sta. Ann. Rep. 397-406. 
1907. East, Edward M., Practical Use of Mendelism in Corn 

Breeding. Conn. (State) Agr. Exp. Sta. Ann. Rep. 406-419. 
1907. Fletcher, S. W., and Gregg, O. I., Pollination of Forced 

Tomatoes. Mich. Agr. Exp. Sta. Spec. Bull. 39. 
1907. Fletscher, F., Mendelian Heredity in Cotton. Jour. 

Agr. Sci. 281-282. 
1907. Gager, C. S., An Occurrence of Glands in the Embryo of 

Zea Mays. Torrey Bot. Club. Bull. 34 : 125-137. 
1907. Gallardo, a., Estudios de Davenport sobre la herencia. 

El Libro (Buenos Aires) 2 : 17-23. 
1907. Gates, R. R., Pollen Development in Hybrids of (Enothera 

lata X 0. Lamarckiana, and its Relation to Mutation. Bot. 

Gaz. 43:81-115, 3 pis. Rev. in Am. Nat. 41:403-404. 



Appendix D 343 

1907. Gregoire, v., Les fondements cytologiques des theories 

courantes sur Vheredite Mendelienne. Soc. Roy. Zool. 

et Malacol. Belgique Ann. 42 : 267-320. 4 figs. 
1907. Gregory, E. S., Pollen of Hybrid Violets. Jour. Bot. 

45 : 377. 
1907. Gregory, R. P., On the Inheritance of Certain Characters 

in Primula sinensis. British Assoc. Adv. Sci. Rep. 691- 

693. 
1907. Hatai, S., Studies on the Variation and Correlation of 

Skull Measurements in Both Sexes of Mature Albino Rats. 

(Mus norvegicus,vax. Albus.) Am. Jour. Anat. 7 : 423-441. 
1907. Heckel, E., Sur Vorigine de la pomme de terre cultivee 

et sur les midations gemmaires culturales des Solanum 

tuberiferes sauvages. Facult. d. Sciences Marseille Ann. 
1907. Hill, A. W., The Natural Hybrid between the Cowslip and 

Oxlip. New Phytolog. 6 : 162. 
1907. Hurst, C. C., MendeVs Law of Heredity. Roy. Hort. 

Soc. Jour. 32 : 227. 
1907. International Confererice on Plant Hardiness and Ac- 
climatization. Science, n.s. 26 : 356-357. 
1907. Johnson, E. W., Sage Brush and Cactus. Am. Bot. 

12 : 59-63. 
1907. Kammerer, Paul, Bastardierung von Flussbarsch [Perca 

ftiwiatilis L.) und Kaulbarsch (Acerina cernua L). Arch. 

f. Entwick'mech. d. Org. 23 : 511-551, 2 pis. & 1 fig. Bib- 

liog. 
1907. Klebs, Georg, Studien iiber Variation. Arch. f. 

Entwick'mech. d. Org. 24 : 2^113, 15 figs. 4 tab. Bibliog. 
1907. Lamb, A. B., A New Explanation of the Mechanics of 

Mitosis. Jour. Exp. Zool. 5 : 27-33. 
1907. Leveille, H., Un nouvel hybride de J uncus. Soc. 

Botan. France Bull. 54 : 517-518. 
1907. Lock, R. H., The Interpretation of Mendelian Phenomena. 

Nature, 76 : 616, 77 : 32. 



344 Plant-Breeding 

1907. Lock, R. H., On the Inheritance of Certain Invisible Char- 
acters in Peas. Roy. Soc, Proc. London B. 79 : 28 pp. 

1907. LuTZ, Anne M., The Chromosomes of (Enothera Lamarck- 
iana and One of its Mutants, 0. gigas. Science, n.s. 26 : 
151-152. Fig. 

1907. MacDougal, D. T., Vail, A. M., & Shull, G. H., Muta- 
tions, Variations, and Relationships of the (Enotheras. Car- 
negie Inst. Pub. no. 81. 1-92. pi. 1-22. & Fig. 1-73. 

1907. MacDougal, D. T., Hybrids among Wild Plants. Plant 
World 10 : 25-37. Figs. 7-8. 

1907. MacDougal, D. T., Hybridization of Wild Plants. Bot. 
Gaz. 43 : 45-58. Figs. 1-4. 

1907. MacDougal, D. T., Natural Hybrids. Plant World, 
10 : 138-139. 

1907. Martinet, M., Experiences sur la selection des cereales. 
Annuaire Agr Suisse, 75. 

1907. MuDGE, G. P., The Interpretation of Mendelian Phenom- 
ena. Nature, 70 : 8. 

1907. Noll, F. Uber eine Heegeri-dhnliche Form der Capsella 
bursa pastoris Mnch. Niederrheinischen GeseU. f. Natur- 
u. Heilk. z. Bonn. Sitzungsber. 

1907. NusBAUM, JozEF, Kleiner Beitrag zur atavistischen 
Regeneration der Sch ren bei Flusskrebse. Arch. f. Ent- 
wick'mech. d. Org. 24 : 124-130, 2 figs. Bibliog. in notes. 

1907. O'Mara, p.. Sports. Hort. Soc. N. Y. Jour. 1 : 39-43. 

1907. Pearl, R., Variation and Differentiation in Ceratophyllum. 
Carnegie Inst. Wash. Pub. 58: (136 pp.), 2 pis., 126 figs. 
Rev. in Am. Nat. 41 : 404-405. 

1907. Reid, a. G., The Interpretation of Mendelian Phenomena. 
Nature, 7 : 566. 

1907. Reitsma, J. F., Correlative variabiliteit bij planten. 
Dissert. 98 pp. Amsterdam. 

1907. RusBY, H. H., Some Little-known Edible Native Fruits 
of the United States. N. Y. Bot. Gard. Jour. 8 : 175, 177-178. 



Appendix D 345 

1907. RusBY, H. H., The Wild Grains and Nuts of the United 
States. Jour. N. Y. Bot. Gard. 7 : 269-273. 

1907. Shamel, a. D., and Cobey, W. W., Tobacco Breeding. 
U. S. Dept. Agr. Bur. Plant Ind. Bull. 96 : 1-67, 10 pis. & 
14 figs. 

1907. Shamel, A. D., The Art of Seed Selection and Breeding. 
U. S. Dept. Agr. Yearbook, 221-236, 5 pis. Same. Year- 
book separate, 446 : 221-236 5 pis. 

1907. Shepard, W. F., The Calculation of the Moments of a 
Frequency Distribution. Biometrika, 5 : 450-459. Rev. in 
Am. Nat. 42 : 418-422. 

1907. Shull, G. H., Results of Crossing Bursa bursa-pastoris 
and Bursa Heegeri. Intern. Zool. Congress, 7th Proc. 
(6 pp.) Boston. Cambridge, Mass. 1910. 

1907. Spalding, V. M., The Artificial Production of Mutants. 
Science, n.s. 26 : 349-350. 

1907. Spillman, W. J., Standardizing Breed Characteristics. 
Soc. for Prom. Agr. Sci. Proc. 28: 116-120. 

1907. Stoll, Ein interessanter Bastard zwischen einem Emmer 
und Kolbenspelze. Deutsche Landw. Presse, 100. 

1907. ViLMORix, Ph. de. Evolution et Selection, theories an- 
ciennes et nouvelles. Paris. Soc. Agr. de France. 

1907. Vries, H. de, Luther Burbank's Ideas on Scientific Horti- 
culture. Century Mag. 73 : 674-681. Illus. 

1907. Vries, H. de. Evolution and Mutation. The Monist, 
17:6. 

1907. Vries, H. de. On Twin Hybrids. Bot. Gaz. 44 : 401- 
407. 

1907. Webber, H. J., and Boykin, F. B., The Advantage of 
Plantiyig Heavy Cotton Seed. U. S. Dept. Agr. Farmers' 
Bull. 285: (16 pp.), 6 figs. 

1907. Wight, W. F., The History of the Cowpea and its Intro- 
duction into America. U. S. Dept. Agr. Bur. PI. Ind. Bull. 
1026:1-21. PI. 1-3. 



346 Plant-Breeding 

1907. Wilson, J. H., The Hybridization of Cereals. Jour. 

Agr. Sci. 2:68. 
1907. Winkler, H., tlber Pfropfbastarde und Uanzlichefl 

Chimdren. Deutsch. Bot. Gesell. Ber. 25 : 568. Rev. 

(Ger.) in Arch. f. Entwick'mech. d. Org. 28 : 163. 

1907. Yule, U., Mendelism and Biometry. Nature, 76 : 152. 

1908. Balls, W. S., Mendelian Studies of Egyptian Cotton. 
Jour. Agr. Sci. 2 : 346-379. 

1908. Beal, W. J., Mutations of Rudbeckia hirts. Am. Ass'n 
Adv. Sci., Sec. Bot. Abstr. in Science, n.s. 27 : 207-208. 

1908. Bennett, B. L., .4 Method of Breeding Early Cotton to 
Escape Boll-weevil Damage. U. S. Dept. Agr, Farmers' 
BuU. 314: (30 pp.), 16 figs. (Including: A description 
of the distinguishing characteristics of early cotton, instruc- 
tion for seed selection, crossing one plant with another, 
treatment to insure a stand, experiments, etc.) 

1908. BiFFEN, R. H., On the Inheritance of Strength in Wheat. 
Jour. Agr. Sci. 3: 86-101. 1 fig. 

1908. Bolley, Henry L., Observations regarding the Constancy 
of Mutants and Questions regarding the Origin of Disease 
Resistance in Plants. Am. Nat. 42: 171-183. Bibliog. 
in notes. 

1908. Briem, H., Naturliche Bastardierungen zwischen Zucker- 
riXben und Futterruben. Oester.-rung. Zeitsch. f. Zuckerin- 
dustrie u. Landw. : (4 pp.). 

1908. Briem, H., Mitteilungen und Bemerkungen zu de Vries, 
zilchtersichen Ansichten. Blatter f . Zuckerriibenbau, 15 : 
309-312. 

1908. Bristol, C. L., Otter Sheep. (Note.) Am. Nat. 42 : 282. 

1908. Bull, C. P , Corn Breeding in Minnesota. Minnesota 
Agr. Exp. Sta. BuU. 173-266. 

1908. Burtt-Davy, J., How to Secure Good Seed-maize. Trans- 
vaal Agr. Jour. 6 : 441-453. 5 pis. 

1908. Cannon, W. A., A Redwood Sport. Plant World, 11 : 232- 
234. 



Appendix D 347 

1908. Clark, Charles C, Wheat Crops of the United States, 
1866-1906. U. S. Dept. Agr. Bur. Statistics BuU. 57: 
(39 pp.) (revised). 

1908. Clute, W. N., The Boston Fern and its Sports. Fern 
BuU. 15 : 73-74. 

1908. Clute, W. N., A Remarkable Change of Color in Trillium. 
Am. Bot. 14 : 33-35. lUus. 

1908. Cobb, J. A., The Effect of Errors of Observation upon the 
Correlation Coefficient. Biometrika, 6 : 109. 

1908. Cockerell, T. D. A., Variation in Helianthus. Bot. 
Gaz. 45 : 338. 

1908. Cook, 0. F., The Mendelian Inheritance of Mutations. 
Science, n.s. 28 : 86-88. 

1908. Cook, 0. F., Reappearance of a Primitive Character in 
Cotton Hybrids. U. S. Dept. Agr. Bur. Plant Ind. Circ. 
18: (11pp.). 

1908. CoRRENS, C, Die Bestimmung und Vererbung des De- 
schlechtes nach neuen Versuchen mit hoheren Pfianzen. Ab- 
stract presented before a recent meeting of the Medico- 
Biological Journal Club of the University of Virginia, by 
H. E. Jordan, adjunct professor of anatomy. Rev. in Am. 
Nat. 42: 811. 

1908. CoRREXS, C, Weitere Untersv^hungen iiber die Geschlechts- 
formen polygamer Bliitenpfianze. Jahr. f. Wiss. Botan. 
45 : 661-700. 

1908. CoTTOX, J. S., The Improvement of Mountain Meadows. 
U. S. Dept. Agr. Bur. Plant Ind. BuU. 127 : (29 pp.), 4 pis. 

1908. Cramer, P. J. S., Mutaties bij Coffea robusta. Teys- 
mannia (Batavia), 19 : 531-537. 

1908. Cramer, P. J. S., De variaties van Coffea liberica in 
Liberia. Teysmannia, 19 : 667-683. 

1908. Cuenot, L., "Les Idees Nouvelles sur VOrigine des Es- 
peces par Mutation.'' Abstr. in Science, n.s. 30 : 768-769. 
Trans, from Rev. gen. Sci. pures et appUq. 19: (Xo. 21). 



348 Plant-Breeding 

1908. CuENOT, L., and Mercier, L., Etudes sur le cancer des 
Souris. Y a-t-il un rapport entre les differ entes muta- 
tions connues chez les souris et la receptivite a la greffef 
Acad. Sci. Paris Compt. Rend. 147 : 1003-1005. 

1908. Cunningham, J. T., The Inheritance of Acquired Char- 
acters. Nature, 77 : 367. 

1908. Dachnowski, A., Type and Variability in the Annual 
Wood-increment of Acer ruhrum L. Ohio Nat. 8 : 343-349. 
Fig. 1. 

1908. Danforth, C. H., Notes on Numerical Variation in the 
Daisy. Bot. Gaz. 46 : 349-356. 

1908. Darbishire, A. D., On the Result of Crossing Round with 
Wrinkled Peas, with Especial Reference to their Starch-grains. 
Roy. Soc. London Proc. B. 80 : 122-135. 

1908. Davenport, C. B., The American Breeder's Association. 
Science, n.s. 27 : 413-417. 

1908. Davenport, C B., Determination of Dominance in 
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1908. Davenport, C. B., Recessive Characters. Science, n.s. 
28: 729. 

1908. Davis, C. A., Some Interesting Variations of Common 
Plants. Michigan Acad. Sci. Rep. 10 : 37-38. 

1908. Dean, Bashford, The Lamarck Manuscript in Harvard. 
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1908. Dix, W., Uher die Entstehung eines Squarehead bei Tri- 
ticum turgidum Weizen. 111. Landw. Zeitg. 837-838. 2 figs. 

1908. Druery, C. T., Natural Selection. Roy. Hortic. Soc. 
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1908. Druery, D. T., The Origin of the Potato. Nature, 79: 
305. 

1908. East, E. M., Suggestions concerning Certain Bud Varia- 
tions. Plant World, 11 : 77-83. 

1908. FioRi, A., Un nuovo ibrido di Carduus {C. simplicif alius 
X nutans Nol). Soc. Bot. Ital. Bull. 155-156. 



Appendix D 349 

1908. Fyson, p. F., Some Experiments in the Hybridising of 

Indian Cottons.^ India Dept. Agr. Mem. Bot. Ser. (29 pp.). 
1908. Gain, E., Etude biometrique sur un hybride de prime- 

veres, Primula flagellicaulis Pax. Assoc. Franc. Avanc. 

Sci. Compt. Rend. 36 : 490. 
1908. Gallardo, a., Sur Vepreuve statistique de la hi de 

Mendel. Acad. Sci. Compt. Rend. 146 : 367-372. 
1908. Gates, R. R., The Chromosomes of (Enothera. Science, 

n.s. 27 : 193-195. Bibliog. in notes. 
1908. Gates, R. R., A Preliminary Account of Studies in the 

Variability of a Unit Character in (Enothera. Am. Ass'n 

Adv. Sci., Sec. Bot. ; Abstr. in Science, n.s. 27 : 209. 
1908. Geerts, J. M., Uber die Zahl der Chromosomen von 

(Enothera Lamarckiana. Deut. Bot. Gesell. Ber 25- 

191. 
1908. Hansen, N. E., Neiv Hybrid Fruits. South Dakota 

Agr. Exp. Sta. Bull. 108: (14 pp.), 9 pi. (Plums.) 
1908. Hardy, G. H., Mendelian Proportions, in a Mixed Popu- 
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1908. Harris, D. F., The Functional Inertia of Living Matter. 

A contribution to the physiological theory of life. 136 pp. 

London. 
1908. Henslow, G., The History of the Cabbage Tribe. Roy. 

Hort. Soc. Jour. 34 : 15-23. 
1908. HiLDEBRAND, F., Ubcr Samlinge von Cijtisus Adamii. 

Deutsch. Bot. Gesell. Ber. 26a : 590-595. 
1908. Hill, E. J., A Red Fruited Huckleberry. Torreya, 8 : 30- 

31 pp. 

1908. Iltis, H., Johann Gregor Mendel als Forscher und Mensch. 
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1908. Jackson, H. S., Development of Disease-resistant Varie- 
ties of Plants. Mass. Hort. Soc. Trans. 123-136. 

1908. Jennings, H. S., Heredity, Variation and Evolution in 
Protozoa II. Heredity and Variation of Size and Form in 



350 Plant-Breeding 

Paramcecium, with Studies of Growth, Environmental Action 

and Selection. Am. Philos. Soc. Proc. 47 : 393-546. 
1908. KoRiBA, K., Variation in the Ray-flowers of Some Com- 

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1908. Kribs, H. G., Note on the Relative Variability of the 

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1908. Leake, H. M., Studies in Experimental Breeding of the 

Indian Cottons; and introductory note. Asiat. Soc. Bengal 

Jour. 13-20. 
1908. Lefevre, J., Contribution a Vhistoire des theories pro- 

posees sur la variation des types vegetaux. Assoc. Franc. 

Avanc. Sci. Compt. Rend. 36 : 426. 
1908. LocHHEAD, W., The Problem of Breeding Disease-resistant 

Plants. Can. Seed-Grow. Assoc. Rep. 4 : 64-70. 2 tabs. 
1908. Lock, R. H., The Present State of Knowledge of Heredity 

in Pisum. Roy. Bot. Gard. Peradeniya Ann. 4:93-111. 
1908. LoLLi, A., Osservazioni su una varieta di Mais ramificato. 

Staz. Sper. Agr. Ital. 41 : 761-767. 1 pi. 
1908. MacDougal, D. T., First Crosses Breeding True. Plant 

World, 11:42. 
1908. McAlpine, D., The Improvement of Cereals by Selection 

and Crossing. Dept. Agr. Victoria Jour. 6 : 282. 
1908. Meyer, P., Les croisements et Vheredite des caracteres 

{la hi de Mendel). Rev. Gen. des Sci. pures et appliquees, 

27-31. 
1908. MiNKiEwicz, R., Uetendue des changements possibles 

de couleur de Hippolyte various. Compt. Rend. Acad. 

Sci. 147 : 943-944. 
1908. Moore, E., Abnormalities in the Radish, Clover, and Ash. 

Torreya, 8 : 220 pp. 
1908. O'Farell, H. H., The Interpretation of Mendelian Phenom- 
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1908. Ortmann, a. E., The Inheritance of Fluctuating Varia- 
tion. Science, n.s. 27 : 545-546. 



Appendix D 351 

1908. Orphal, K., Untersuchungen uher Korrelation-ser- 
scheinungen bei mehreren. Sorten der Vicia Faba. Jena. 
75 pp. 

1908. Orton, W. a., The Development of Farm Crops Resistant 
to Disease. U. S. Dept. Agr. Yearbook, 453-464. 2 pis. 
Same. Yearbook separate, 494 : 453-464. 2 pis. 

1908. Paulin, G., No Struggle for Existence, no Natural Selec- 
tion. Critical examination of the fundamental principles 
of the Darwinian theory. 284 pp. London. 

1908. Pearl, Raymond (Reviewer), Biometrics. Recent con- 
tributions to theory. (Review.) Am. Nat. 42 : 418-422. 
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1908. Price, H. L., and Drinkard, A. W., Inheritance in 
Tomato Hybrids. Virginia Agr. Exp. Sta. Bull. 177 : 15^ 
54. PI. Fig. 

1908. PuNNETT, R. C, Mendelism in Relation to Disease. Roy. 
Soc. of Med. Proc. Epidemiol. Sect. 1 : 83-168. 

1908. Reid, G. a., Mendelism and Sex. Nature, 77 : 236- 
237. 

1908. Reid, G. A., The Inheritance of "Acquired^' Characters. 
Nature, 77 : 442. 

1908. RoBBiNs, W. W., Variation in Flower-heads of Gaillardia 
aristate. Biometrika, 6 : 106-108. Fig. Diagr. 

1908. Rolfe, R. a., and Hurst, C. C., The Orchid Stud-book. 
Enumeration of hybrid orchids of artificial origin, with 
their parents, raisers, rate of first flowering, etc. xlvi 
+ 325 pp. Kew. 121 figs. 

1908. RosENAu, J., and Anderson, J. F., Further Studies 
upon Hyper susceptibility and Immunity. Jour, of Med. Re- 
search, Vol. 16, pp. 381-418. Rev. in Am. Nat. 42 : 135. 

1908. Seaver, F. J., Color Variation in some of the Fungi. 
Torrey Bot. Club Bull. 35 : 307-314. 

1908. Shimek, B., a Hybrid Oak. Iowa Acad. Sci. Proc. 15: 
77-83, pis. 1-2. 



352 Plant-Breeding 

1908. Shull, G. H., Dr. Baur on Variegation. Plant World, 

11 : 147-151. 
1908. Shull, G. H., The Pedigree Culture, its Aims and Methods. 

Plant World, 11:21. 
1908. Shull, G. H., Some New Cases of Mendelian Inheritance. 

Am. Ass'n Adv. Sci., Sec. Bot. ; Abstr. in Science, n.s. 

27 : 206. 
1908. Shull, G. H., Some New Cases of Mendelian Inheritance. 

Bot. Gaz. 45: 103-116, figs. 1-4. 
1908. Shull, G. H., A New Mendelian Ratio and Several Types 

of Latency. Am. Nat. 42: 433-451. Bibliog. in notes. 
1908. Sutton, Arthur W., Brassica Crosses. Linnean Soc. 

Bot. Jom\ 38:337-349. 12 pis. Rev. in Zeitsch. f. ind. 

Abs. u. Vererb. 2 : 140. 
1908. Terry, W. A., A New Variety of the Ostrich Fern. Fern 

Bull. 16:3-4. 
1908. Trail, J. W. H., Floral Variation in the Genus Veronica. 

Scottish Nat. Hist. Soc. Ann. 68 : 158-259. 
1908. TscHERMAK, E. VON, Die Mendelschen V ererhurgegesetze. 

Schr. zur Verbr. Naturwiss. Kennt. (Wien.) 48 : 145-164. 
1908. TscHERMAK, E. VON, Dcr Moderne Stand des Vererhungs- 

proble^ns. Arch. f. Rassen- und Ges.-Biol. 5 : 305-326. 
1908. Vries, H. de, Especes et varietes; leur naissance par 

mutation. Trad, de I'angl. p. L. Blaringhem. Paris. 
1908. Vries, H. de, Uber die Z willing sbastarde von (Enothera 

nanella. Deutsch. Bot. Gesells. Ber. 26a : 667-676. 
1908. Webber, H. J., Plant Breeding for Farmers. Cornell 

Univ. Agr. Exp. Sta. Bull. 251 : 282-332. 
1908. Webber, H. J., Improving Corn by Seed Selection. Cor- 
nell Univ. Farmers' Reading Course Bull. 42 : 5. Figs. 
1908. Werner, F., Nochmals Mimikry und Schutzfdrbung. 

Biol. Centralbl. 28 : 567-576, 588-601. 
1908. White, C. A., Aggregate Mutation of Gossypium. Science, 

n.s. 27 : 193. 



Appendix D 353 

1908. WiCKSON, E. J., Luther Burbank and his New Environment. 

Sunset Mag. 27 : 151-162. 
1908. WiLLisTON, S. W., What is a Species? Am. Nat. 42: 

184-194. 
1908. Winkler, Hans, Uber Parthenogenesis und Apogamie 

im Pflanzenreiche. Prog. Rei. Bot. 2 : 293-454. Fig. 

Bibliog. 
1908. Winkler, H., Solanum tubingense, ein echter Pfropf- 

bastard zwischen Tomate und Nachtschatten. Deutsch. 

Bot. Gesell. Ber. 26a : 595-608. 2 illus. 
1908. Winkler, H., Parthenogenesis und Apogamie im Pflan- 

zenreich ( — in the plant kingdom), 166 pp. Reprint 

from Prog. Rei. Bot. 2 ; Rev. (Ger.) in Arch. f. Entwick'- 

mech. d. Org. 26 : 696. 

1908. Zavitz, C. a., The Work of Plant Improvement at Home 
and Abroad. Can. Seed-Grow. Assoc. Rep. 4 : 42-46. Tab. 

1909. Aaronsohn, A., Contribution a Vhistoire des cereales. 
Le ble, Vorge et le seigle a Vetat sauvage. Soc. Bot, France 
Bull. 56 : 196-203, 56 : 237-245, 56 : 251-258. 

1909. Aikman, p. J. A., Oii Some Hybrid Tuberous Solanums. 

Roy. Hort. Soc. Jour. 35 : 53-55. 
1909. Baco, F., Sur des variations de vignes greffees. Acad. 

Sci. Paris, Compt. Rend. 148:429-431. 
1909. Balls, Lawrence, Some Cytological Aspects of Cotton 

Breeding. A. B. A. Rep. 5: 16-29. 
1909. Bateson, W., Saunders, Miss E. R., Punnett, R. C., 

Experimental Studies in the Physiology of Heredity. Roy, 

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f. ind. Abs.- u. Vererb. 2 : 17-19. 
1909. Bateson, W., Mendel's Principles of Heredity. 396 pp. 

G. P. Putnam's Sons, N. Y. Cambridge (England) Univ. 

Press. 6 pis., 35 figs., 3 plates. Rev. in Science, n.s. 30: 

481-483. 

1909. Baur, E., Die Aurea-Sippen von Antirrhinum majus. 
2a 



354 Plant-Breeding 

Zeitsch. f. indukt. Abst.- u. Vererb. 1 : 124-125. Bibliog. 

in notes. 
1909. Bauer, E,, Pfropfbastarde. Periklinalchimdren und 

Hyperchimdren. Deutsch. Bot. Gesell. Ber. .27 : 603-605. 
1909. Beach, S. A., The Present Status of Apple Breeding in 

America. A. B. A. Rep. 5 : 28-36. 
1909. Bellair, G., L' hybridation en horticulture. 350 pp. 

Paris, 123 figs. 
1909. Benedict, R. C, N'eiv Hybrids in Dryopteria. Torrey 

Bot. Club Bull. 36 : 41-49. Includes D. Cintoniana X 

spinuloss, D. cristata X Goldiana, D. Goldiana X spinulos 

and D. intermedia X marginalis hybb. nov. 
1909. Blaringhem, L., Sur les hybrides d'orges et la hi de 

Mendel. Acad. Sci. Paris, Compt. Rend. 148 : 854-857. 
1909. Boas, Franz, Determination of the Coefficient of Correla- 
tion. Science, n.s. 29 : 823-824. 
1909. Broomall, cm., Flower Pigments. Delaware County 

Inst. Sci. Proc. 4 : 81-84. 
1909. Brown, Harry R., Selection of Seed Potatoes. Can. 

Seed-Grow. Assoc, Rep. 5 : 103-105. 
1909. Brozek, a., Variabilitdt bei Palcemonetes varians. 

Bohm Ges. Wiss. Prag. S. B. 1-11. 
1909. Burtt-Davy, J., Mendelism in Maize. Transvaal Agr. 

Jour. 7 : 461-462. 
1909. Bybowski, J., Regeneration des plajitations de cafeiers 

par V introduction d'une espece nouvelle. Acad. Sci. 

Paris, Compt. Rend. 148 : 232-235. 
1909. Cannon, W. A., Studies in Heredity as Illustrated by the 

Trichomes of Species and Hybrids of Juglans, (Enothera, 

Papaver and Solajium. Carnegie Inst. Wash. Pub. 117. 

Washington, D.C., pis. 1-10, and figs. 1-21. 
1909. Carleton, M. A., Field Methods in Wheat Breeding. 

A. B. A. Rep. 5 : 185-207. 
1909. Castle, W. E., The Behavior of Unit Characters in Heredity. 



Appendix D 355 

In Fifty Years of Darwinism, pp. 143-159. Bibliograph. 

in notes. 
1909. Chambers, Robert, Einfluss der Eigrosse und der Tem- 

peratur auf das Wachsthum und die Grosse des Frosches 

und dessen Zellen. Arch, fiir Mikroskopische Anatomic 

und Entwicklungsgeschichte ? Vol. 72, pt. 3, pp. 607-661. 

Rev. in Am. Nat. 43:57. 
1909. Chamblise, Charles E., A Note on Rice Breeding. 

A. B. A. Rep. 5 : 182-185. 
1909. Clothier, Geo. L., Practical Possibilities of Grafting 

and Building Forest and Nut Trees. A. B. A. Rep. 5 : 262- 

265. 
1909. Collins, G. N., The Importance of Broad Breeding in 

Corn. Dept. Agr. Bur. Plant Ind. 141 (pt. 4) : 33-44. 
1909. Cook, 0. F., McLachlan, Argyle, and Meade, Row- 
land M., A Study of Diversity in Egyptian Cotton. U. S. 

Dept. Agr. Bur. Plant Ind. Bull. 156: (60 pp.), 6 pis. 
1909. Cook, O. F., Pure Strains as Artifacts of Breeding. Am. 

Nat. 43 : 241-242. 
1909. Cook, 0. F., Suppressed and Intensified Characters in 

Cotton Hijhrids. U. S. Dept. Agr. Bur. Plant Ind. Bull. 

147: (27 pp.). 
1909. Cook, 0. F., The Superiority of Line Breeding over Narrow 

Breeding. U. S. Dept. Agr. Bur. Plant Ind. Bull. 146: 

(45 pp.). 
1909. Criddle, N., The So-called White Wild Oats and What 

they Are. Ottawa Nat. 23 : 127-128. 
1909. Darbishire, A. D., An Experiinental Estimation of the 

Theory of Ancestral Contributions in Heredity. Roy. Soc. 

London Proc. 81 : 61-79. 
1909. Darbishire, A. D., Recent Advances in the Study of 

Heredity. III. New Phytolog. 7 : 157-181 ; 7 : 237-248. 
1909. Davenport, Charles B., Mutation. In Fifty Years of 

Darwinism, pp. 160-181. 



356 Plant-Breeding 

1909. De Loach, R. J. H., The Problem of Fixation in Cotton 
Hybrids. A. B. A. Rep. 5 : 130-138. 

1909. Demoll, R., and Strohl, J., U influence de la tem- 
perature sur le developpeinent des organismes et la duree 
de la vie. Soc. Biol. Compt. Rend. 66 : 855-857. 

1909. Dow, George, Some Results Obtained through the Careful 
Selection of Seeds. Can. Seed-Grow. Assoc. Rep. 5 : 109- 
111. 

1909. East, E. M., A Study of the Factors Influencing the Im- 
provement of the Potato. III. Exp. Sta. Bull. 127 : Rev. 
in Zeitsch. f . ind. Abs.- u. Vererb. 2 : 142-143. 

1909. East, E. M., Note concerning Inheritance in Sweet Corn. 
Science, n.s. 29 : 465-467. 

1909. East, Edward M., The Distinction between Development 
and Heredity in Inbreeding. Am. Nat. 43 : 173-181. Bib- 
liog. in notes. 

1909-10. East, E. M., The Transmission of Variations in the 
Potato in Asexual Reproduction. (Contr. from the Labora- 
tory of Genetics, Bussey Institution of Harvard University, 
No. 3.) Conn. Exp. Sta. Rep. 120-160, 5 pis. 

1909. Emerson, R. A., Factors for Mottling in Beans. A. B. A. 
Rep. 5 : 368-376. 

1909. Emerson, R. A., Inheritance of Color in the Seeds of the 
Common Bean, Phaseolus vulgaris. Nebraska Agr. Exp. 
Sta. Rep. 22:65-101. 

1909. Forbes, F. E., A New Hybrid Violet. Rhodora, 11: 
15-15. V. Brittoniana X lanceolata. 

1909. Garner, W. W., Breeding Tobacco for High and Low 
Nicotine Conte7it. A. B. A. Rep. 5 : 299-303. 

1909. Gates, R. R., A] Litter of Hybrid Dogs. Science, n.s. 
29:744-747. Tab. ^ 

1909. Gates, R. R., The Behavior of the Chromosomes in (Eno- 
thera lata X 0. gigas. Bot. Gaz. 48 : 179-199, pis. 12-14. 

1909. Gates, R. R., The Stature and Chromosomes of (Enothera 



Appendix D 357 

gigas De Vries. Archiv Zellforsch. 3 : 525-552. Pis. 

29-30. 
1909. Gatin, M. C. L., La morphologie de la germination et 

ses rapports avec la phylogenie. Rev. Gen. Bot. 21 : 147- 

158. 
1909. Geerts, J. M., Beitrdge zur Kenntnis der Cytologie und 

der partiellen Sterilitdt von (Enothera Lamarckiana. Rec. 

Trav. Bot. Neerlandais, 5: 1-114, 28 pis. 
1909. Griffon, E., Recherches sur la xenie chez les Solanees. 

Soc. Bot. France Bull. 55 : 714-720. 
1909. Guthrie, C. C., Guinea Pig Grajt-hyhrids. Science, 

n.s. 30 : 724-725. Bibliog. in notes. 
1909. Hagedoorn, Arend L., Mendelian Inheritance of Sex. 

Arch. f. Entwick'mech. d. Org. 28 : 1-34, 3 figs. 
1909. Hansen, N. E., The Wild Alfalfas and Clovers of Siberia, 

with a Prospective View of the Alfalfas of the world. U. S. 

Dept. Agr. Bur. Plant Ind. Bull. 150: (31 pp.), 1 pi. 
1909. Harris, J. A., Variation in the Number of Seeds per Pod 

in the Broo7n, Cytisus scoparius. Am. Nat. 43 : 350-355, 

2 tab. Diag. Bibliog. in notes. 
1909. Harris, J. A., A Short Method of Calculating the Coefficient 

of Correlation in the Case of Integral Variates. Biometrika, 

7:214-218. 
1909. Harris, J. A., Note on Variation in Adoxa. Biometrika, 

7 : 218-222. 
1909. Harris, J. A., The Correlation between Length of Flower- 
ing Stalk and Number of Flowers per Inflorescence in Nothos- 

cordum and Allium. Missouri Bot. Gard. Rep. 20 : 105-115. 
1909. Harris, J. A., Variation and Correlation in the Flowers 

of Lagerstroemia indica. Missouri Bot. Gard. Rep. 20 : 

97-104. 
1909. Harshberger, J. W., The Biologist's Part in Practical 

Plant and Animal Breeditig. Amer. Vet. Rev. 35 : 254- 

265. 



358 Plant-Breeding 

1909. Meckel, M., Fixation de la mutation gemmaire culturale 
du Solanum maglia. Soc. Nation. d'Agr. Bull. 69 : 874-877. 

1909. HoLDEFLEiss, P., Bastardierimgsversuche mit Mais. 
Landwirtsch. Inst. Halle a. S. Ber. 19 : 178-198, 1 pi. 

1909. Holmes, S. J., The Categories of Variation. Am. Nat. 
43 : 257-285. 

1909. Howard, A., and Howard, G. L. C, The Varietal Char- 
acters of Indian Wheats. India Dept. Agr. Mem. Bot., 
Series 2: (66 pp.). 

1909. Hy, F., Sur une forme sterile de Cardamine hirsuta. 
Soc. Bot. France Bull. 56: 210-213. 

1909. Jennings, S. H., Heredity and Variation in the Simplest 
Organism. Am. Nat. 43 : 321-337. Bibliog. in notes. 

1909. Jepson, Willis L., Spontaneous Hybrids of Native Cali- 
fornian Trees. A. B. A. Rep. 5 : 259-262. 

1909. Johannsen, W., Uber Knospenmutation bei Phaseolus. 
Zeitsch. f. indukt. Abst.- u. Vererb. 1 : 1-10, 2 figs. Bib- 
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1909. Johnson, R. H., Variation in Syndesmon and Hepatica. 
Ohio Nat. 9:431-436. 

1909. JoRDON, D. S., and Kellogg, V. L., The Scientific As- 
pects of Luther Burbank's Work, xiv + 115 pp. San 
Francisco. 

1909. Knuth, R., liber Bastardbildung in der Gattung Pelargo- 
nium. Bot. Jahrb. f. Systematik usw. (Engler) 44 : 1-35. 
4 figs. 

1909. Leake, H. M., Studies m the Experimental Breeding of 
Indian Cottons 2. On Buds and Branching. Asiat. Soc. 
Bengal Jour., n.s. 5 : 23-30. 

1909. Leavitt, R. G., A Vegetative Mutant and the Principle 
of Homoeosis in Plants. Bot. Gaz. 47 : 30-68, figs. 1-19. 

1909. Lee, F. E., Report of Wheat Improvement Committee. 
Dept. Agr. Victoria Jour. 7 : 239-254. 

1909. Lock, R. H., A Preliminary Survey of Species Crossing 



Appendix D 359 

in the Genus Nicotiana from the Mendelian Standpoint. 
Roy. Bot. Gard., Peradeniya Annals, 4 : 195-227, 12 pis. & 

Ifig. 

1909. Love, Harry H., Influence of Food Supply on Variation. 
A. B. A. Rep. 5:357-365. 

1909. Macallum, a. B., On the Origin of the Life on the Globe. 
Canadian Inst. Trans. 8 : 423-441. 

1909. MacDougal, D. T., The Direct Influence of Environment. 
In Fifty Years of Darwinism, pp. 114-142, 2 pis. Bibliog- 
raphy in notes. 

1909. McAlpine, D., and de Castella, F., Bud-variation in 
Corinth Currant Vine. Victoria Dept. Agr. Jour. 7 : 145- 
149. 

1909. McCallum, W. B., The Reciprocal Influence of Scion 
and Stock. Plant World, 12 : 281-286. 

1909. Marryat, (Miss) Dorothea C. E., Hybridisation Ex- 
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1909. Martius, Fr., Das pathogenetische Vererbungsproblem. 4- 
(letztes) Heft der " Pathogenese innerer Krankheiten.^' Nach 
Vorlesungen fiir Studierende und Arzte. pp. 323-467. 
Leipzig und Wien. 

1909. Maynard, G. D., Variability in Shirley Poppies from 
Pretoria. Biometrika, 7 : 227-230. Fig. 

1909. Meisenheimer, Johannes, Experimenielle Studien zur 
Soma und Geschlechts-Differenzierung. Erster Beitrag. 
Jena, Gustav Fischer. Rev. in Am. Nat. 44 : 316. 

1909. Merzbacher, L., Gesetzmassigkeiten in der Vererbung 
und Verbreitung verschiedener hereditdrfamilidrer Erkran- 
kungen. Archiv f. Rassen- u. Gesell.-Biologie, 6 : 172-198, 
2 pis., 19 figs. 

1909. Newman, L. H., Certain Biological Principles and their 
Practical Application in the Improvement of the Field Crops 
of Canada. Ottawa Nat. 23 : 85-91 ; 23 : 105-110. 



360 Plant-Breeding 

1909. Paton, J. Airman, Notes on Some Hybrid Tuberous 
Solariimis. Roy. Hort. Soc. Jour. 35 : 53-55. 

1909. Pearl, Raymond, A Note on the Degree of Accuracy of 
Biometric Constants. Am. Nat. 43 : 238-240. 

1909. Pearl, Raymond, and Surface, Frank M., Selection 
Index Nuynbers and their Use in Breeding. Am. Nat. 
43 : 385-400. 

1909. Pearl, Raymond, and Surface, Frank M., Data on the 
Inheritance of Fecundity obtained from the Records of Egg 
Production of the Daughters of "200-egg " Hens. Maine 
Agr. Exp. Sta. Bull. 166: (34 pp.), 13 figs. 

1909. Pearson, Karl, Determination of the Coefficient of Cor- 
relation. Science, n.s. 30 : 23-25. 

1909. Pearson, K., On the Ancestral Gametic Correlations of 
a Mendelian Population Mating at Random. Roy. Soc. 
London Proc. 81 : 225-229. 

1909. Perriraz, J., Etude hiologique et biometrique sur Nar- 
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176. 

1909. Piper, C. V., Alfalfa and its Improvement by Breeding. 
A. B. A. Rep. 5:94-115. 

1909. Plate, L., Darwinismus u. Landwirtschaft. 24 pp. 
Parey, Berlin. 

1909. Powers, H. J., Are Species Realities or Concepts Only? 
Am. Nat. 43: 598-610. 

1909. Price, H. L., and Drinkard, W., Inheritance in Tomato 
Hybrids. Plant World, 12 : 10-18, figs. 1-2. 

1909. Price, H. L., and Drinkard, A. W., Inheritance in 
Tomato Hybrids. Virginia Agr. Exp. Sta. Bull. 177 : 17- 
53, 10 pis. Rev. (English) in Zeitsch. f. indukt. Abst.- u. 
Vererb. 1 : 402-403. 

1909. RiTTER, G., tfber discontinuierliche Variation im Organis- 
menreiche. Bot. Centralbl. Beih. 251 : 1-29. 

1909. RiTTER, W. E., The Hypothesis of ''Presence and Ab- 



Appendix D 361 

sence " in Mendelian Inheritance. Science, n.s. 30 : 367- 

368. 
1909. Rosenberg, 0., Uber die Chromosomenzahlen bei Taraxa- 
cum und Rosa. Svensk Bot. Tidskr. 3 : 150-162. 
1909. Roux, G., Les problemes de Vheredite. La Revue (Oct. 

1): 375-383. 
1909. RussEL, E. S., The Transmission of Acquired Characters. 

Rivista di Scienza, 5: 192-203. 
1909. Sandsten, E. P., Improvement of Wisconsin Tobacco 

through Seed-selection. Wisconsin Agr. Exp. Sta. Bull 

176. 
1909. Sauer, L. W., Quercus Leana; a Hybrid Oak. Plant 

World, 12: 198-201, figs. 1-2. 
1909. Saxton, W. T., Parthenogenesis in Pinus Pinaster. 

Bot. Gaz. 47 : 406-409, figs. 1-7. 
1909. Seyot, p. M., Etude biometrique des pepins d'un Vitis 

vinifera franc de pied et greffe. Acad. Sci. (Paris) Compt. 

Rend. 149 : 53-56. 
1909. Shoemaker, D. N., Report of the Committee on Breeding 

Cotton. A. B. A. Rep. 5: 115-116. 
1909. Shull, G. H., a Simple Chemical Device to Illustrate 

Mendelian Inheritance. Plant World, 12 : 145-152. Illus. 
1909. Smith, J. Russell, Elimination of the Gullied Hillside 

through Tree Breeding. A. B. A. Rep. 5 : 265-269. 
1909. Spillman, W. J. (Reviewer), The Nature of ''Unit'' 

Characters. (Review.) Am. Nat. 43 : 243-248. Bibliog. 
in notes. 
1909. Spillman, W. J., The Effect of Different Methods of Selec- 
tion on the Fivation of Hybrids. A. B. A. Rep. 5 : 341-347. 
1909. Stevens, F. L., and Hall, J. G., Variation of Fungi 

Due to Environment. Bot. Gaz. 48 : 1-30, figs. 1-37. 
1909. Straugin, M. N., and Church, C. G., The Influence of 
Environment on the Composition of Sweet Corn, 1905-1908. 
U. S. Dept. Agr. Bur. Chemistry Bull. 127 : (69 pp.), 11 figs. 



362 Plant-Breeding 

1909. SuDWORTH. Geo. B.. Prelim. Rep. Chairman Committee on 

Breeding Xut and Forest Trees. A. B. A. Rep. 5 : 255-259. 
1909. Tedix, H., Redogdrelse for arbetena pa Svalof med korn, 

arter och vieker under ar. Sveriges Utsadesfor. Tidskr. 

20:245-255. 1910. 
1909. Trabut. Contribution a Vetude de Vorigine des avoines 

cultivees. Acad. Sci. Paris Compt. Rend. U9 : 227-229. 
1909. Tracy, J. E. ^A'.. Work conducted by the United States 

Department of Agriculture in breeding Highgrade Strains 

of Sugar Beet Seed and testing Important Varieties. A. B. A. 

Rep. 5:284-2S5. 
1909. Trow. A. H.. Forms of Senecio vulgaris. Jour, of Bot. 

47 : 304-306. 
1909. TscHER^L^K. E. v.. Der Moderne Stand der Kreuzungs- 

zuchtung der landwirtschaftlichen Kulturpflanzen. Vortrag 

gehalten in der Okonomischen Gesellschaft in Konigreich 

Sachsen zu Dresden am 5. Feb. 19 pp. 
1909. TscHER^L\K. E. v., Uber Correlationen. Landw. Um- 

schaii, 1 : (2 pp.). 
1909. Van Fleet. W., Report of the Committee on Breeding 

Roses. A. B. A. Rep. 5 : 14-15. 
1909. VoGT, O., Studien ilber das Artproblem. 1. ]\litt. Uber 

das Variieren der Hummeln. 1. Teil. Ges. Xaturf. Freunde 

Berlin Sitzungsber. 28-83, 1 pi. & fig. 

1909. VoLL^L\xx. F.. Die Bedeutung der Bastardierung filr 
die Entstehung von Arten und Formen in der Gattung Hiera- 
cium. Bayer Bot. Gesell. Ber. 12 : 29-37. 

1909. Vries. H. de, Fertilization and Hybridization. ^Monist, 
19 : 514-555. 

1909. Vries, H. de, On Triple Hybrids. Bot. Gaz. 47 : 1-8. 

1909. Vries, H. de. Transformwme et mutation. Rev. du 

Mois. (Sept.), 269-302. 
1909. Wagx'er. a.. Die drei Elemente der Lamarckschen Lehre. 

Zeitsch. Ausbau Entw. Lehre, 3 : 44-60. 



Appendix D 363 

1909. Warburton, C. W., Improvement of the Oat Crop. U. S. 
Dept. Agr. Bur. Plant Ind. Circ. 30 : (10 pp.). 

1909. Waugh and Shaw, Variation in Peas. Mass. (State) 
Agr. Exp. Sta. Ann. Rep. 167-173. 

1909. Webber, H. J., Improving Corn by Seed Selection. Cor- 
nell Univ. Reading-Course for Farmers, 42. 

1909. Webber, H. J., Methods of Breeding and Improving the 
Potato Crop. Cornell Univ. Farmers' Reading-Course 
Bull. 43 : 3 figs. 

1909. Webber, H. J., Clonal or Bud Variation. A. B. A. 
Rep. 5:347-357. 

1909. WEisiL\xx, August, The Selection Theory. Darwin and 
Mod. Sci. pp. 18-65, pL, fig. Bibliog. in notes. 

1909. Westgate, J. M., Methods of Breeding Alfalfa by Selec- 
tion. A. B. A. Rep. 5 : 144-166. 

1909. Westgate, J. M., Another Explanation of the Hardiness 
of Grimm Alfalfa. Science, n.s. 30 : 18^186. 

1909. Wheldale, (Miss) ]\I., The Colours and Pigments of 
Flowers, with Special Reference to Genetics. Roy. Soc. 
London Proc. 81 : 44-60. 

1909. Wheldale, (Miss) M., Further Observations upon the 
Inheritance of Flower-colour in Antirrhinum majus. Roy. 
Soc. London Evol. Comm. Rep. 5 : 1-26. Tables. Bib- 
liog. in notes. 

1909. Wilson, Edmund B., Studies on Chromosomes V. The 
Chromosomes of Metapodius. A Contribution to the Hypothesis 
of the Genetic Continuity of Chromosomes. Jour. Exp. Zool. 
6 : 147-205, 1 pi. & 13 figs. 

1909. Wilson, Edmund B., The Cell in Relation to Heredity 
and Evolution. In Fifty Years of Darwinism, pp. 92- 
113. 

1909. WooDHEAD, J. W., and Drierley, M. M., Development 
of the Climbing Habit in Antirrhinum majus. Xew Pliy- 
tologist, 8 : 284-298, 3 pis. & 5 figs. 



364 Plant-Breeding 

1909. Woodruffe-Peacock, E. A., Heredity of Acquired 

Characters. Jour, of Bot. 47 : 320-321. 
1909. Wright, R. P., Potatoes, Effect of Planting Sprouted 

Tubers on Yield. West. Scot. Agr. Coll. Ann, Rep. 9: 101. 

Roy. Hort. Soc. Abs. in Jour. 35 : 557. 
1909. Zavitz, Z. a., Fotmdation Stock on Plant Breeding. 

A. B. A. Rep. 5: 167-171. 

1909. ZiMMERMANN, W., Orckis coriophora X morio. Allg. 
Bot. Zeitsch. 15: 150-151. 

1910. Andrews, F. M., Twin Hybrids {Iceta and velutina) and 
their Anatomical Distinctioris. Bot. Gaz. 50 : 193-201. 

1910. Babcock, Ernest B., Walnut-Oak Hybrid Experiments. 

Am. Breed. Mag. 1 : 200-202. Tab. 
1910. Ball, Carleton R., The Breeding of Grain Sorghums. 

Am. Breed. Mag. 1 : 283-293. 
1910. Balls, W. L., Some Complications in Mendelian Cotton 

Breeding. Inst. Egyptien Bull. 3 : 120-127. 
1910. Baltzer, F., Uber die Beziehungenzwischen dem Chroma- 
tin und der Eritwickelung und Vererbungs-richtung bei 

Echinodermenbastarden. Arch. Zellforschung, 5 : 497-621. 

5 pis. & 19 figs. 
1910. Barus, C, Variations Graphically. Science, n.s. 31 : 

867-868. 
1910. Bataillon, E., Contribution a V analyse experimentale 

des phenomenes karyocinetiques chez Ascaris megalocephala. 

Arch, f . Entwick'mech. d. Org. 30 : 1 : 24-44, 1 pi. Bib- 

liog. \\ pp. 
1910. Baur, E., Pfropf bastards. Biol. Centralbl. 30:497-514. 

7 figs. 
1910. Benedikt, Moriz, Biomechanische Grundfragen. Of- 

fenes- Sendschreiben an Herrn H of rat Ernst Ludwig. Arch. 

f. Entwick'mech. d. Org. 31 : 164-174. 
1910. Bernard, Noel, L'origine de la pomme de terre. 19 pp. 

Soc. Franc. d'Impr. et de Librairie, Poitiers. Reprint 



Appendix D 365 

from Soc. Acad. d'Agric, Belles] ettres, Sci. et Arts de 
Poitiers Bull. 
1910. Berthault, p., i propos de Vorigine de la pomme de 

terre. Rev. G^n. Bot. 22 : 345-353. 
1910. Berthault, P., Sur les types sauvages de la pomme de 
terre cultivee. Acad. Sci. Paris, Compt. Rend. 150:47- 
50. 

1910. Bessey, E. a.. Air Drainage as Affecting the Acclimatiza- 
tion of Pla7its. N. Y. Hort. Soc. Mem. 2: 25-28. 

1910. Blanchard, Henry F., Improvement of the Wheat Crop 
in California. U. S. Dept. Agr. Bur. Plant Ind. Bull. 178 : 
(37 pp.), 10 figs. ^ 

1910. Bordage, E., a propos de Vheredite des caracteres ac- 
quis. Bull. Scient. France et Belgique 44: (Heft 1). 

1910. Bornet, E., and Gard, M., Recherches sur les hybrides 
artificiels de Cistes obterius par M. Ed. Bornet. I. Notes 
inedites et resultats experimentaux. Ann. des Sci. Natu- 
relles (Botanique) 12 : 71-116. 

1910. Brand, Charles J., The Utilization of Crop Plants in 
Paper Making. U. S. Dept. Agr. Yearbook, 329-340. 
Same. Yearbook Separate, 541 : 329-340. 

1910. Bruce, A. B., The Mendelian Theory of Heredity arid the 
Augmentation of Vigor. Science, n.s. 32:627-628. 

1910. Bruce, A. B., Self-fertilization and Loss of Vigour. Na- 
ture. March 3. 

1910. Buder, J., Pfropfbastarde und Chimaeren. Zeitsch. f. 
allg. Physiol. 11: 15-31. 

1910. Buder, J., Studien an Laburnum Adami. Deutseh. Bot. 
Gesell. Ber. 28: 188-192. 

1910. Burtt-Davy, J., A Note on the Correlation of Characters 
in Maize Breeding. Transvaal Agr. Jour. 8 : 453-455. 

1910. Burtt-Davy, J., An Experiment in Breeding a Neiv Type 
of Maize. Transvaal Agr. Jour. 8 : 450-453. 

1910. Chevalier, J., Influence de la culture svr la teneur en 



366 Plant-Breeding 

alcaloides de quelques Solanees. Acad. Sci. Paris Compt. 
Rend. 150:344-347. 

1910. Clark, Chas. F., Variation and Correlation in Timothy. 
Cornell Univ. Agr. Exp. Sta. Bull. 279 : 421-469, 40 figs. 

1910. Clements, F. E., The Real Factors in Acclimatization. 
N. Y. Hort. Soc. Mem. 2 : 37-40. 

1910. Clothier, Geo. L., Breeding to Improve Physical Quali- 
ties of Timber. Am. Breed. Mag. 1 : 261-263. 

1910. CocKERELL, T. D. A., A New Variety of the Sunflower. 
Science, n.s. 32: 384. 

1910. CoiT, J. E., The Relation of Asexual or Bud Mutation to 
the Decadence of California Citrus or Deads. Fruit Growers' 
Cons. (Cal.) Proc. 37: 31-39. 

1910. Collins, G. N., Increased Fields of Corn from Hybrid 
Seed. U. S. Dept. Agr. Yearbook, 319-328. Same. 
Yearbook Separate, 540: 319-328. 

1910. Collins, G. N., The Value of First-Generation Hybrids 
in Corn. U. S. Dept. Agr. Bur. Plant Ind. Bull. 191: 
(45 pp.). 

1910. CoTTE,' J., and Cotte, C, Sur Vindigenat du ble en 
Palestine. Soc. Bot. France Bull. 56 : 538-540. 

1910. CouPiN, H., Sur la vegetation de quelques moisissures 
dans Vhuile. Acad. Sci. Paris Compt. Rend. 150:1192- 
1193. 

1910. Crosby, Dick J., and Howe, F. W., School Lessons on 
Corn. U. S. Dept. Agr. Farmers' Bull. 409 : (29 pp.), 12 figs. 
(This bulletin contains outlines for class studies and exer- 
cises on the growth and structure of the corn plant, selection 
and testing of seed corn, and the cultivation and breeding of 
corn, with list of publications on the subject.) 

1910. Crosby, Dick J., School Exercises in Plant Production. 
U. S. Dept. Agr. Farmers' Bull. 408: (48 pp.), 39 figs. 
(This bulletin describes the material needed for laboratory 
exercises in plant production, and contains outlines of 



Appendix D 367 

lessons in the structure and growth of plants, methods of 

propagation, seed testing, etc., and a list of publications 

on agriculture, of special interest to teachers.) 
1910. Dachnowski, a., Physiologically Arid Habitats and 

Drought Resistance in Plants. Bot. Gaz. 49 : 325-339. 
1910. Derr, H. B., a New Awnless Barley. Science, n.s. 

32 : 473-474. 
1910. DiLLMAN, Arthur C, Breeding Drought-Resistant Forage 

Plants for the Great Plains Area. U. S. Dept. Agr. Bur. 

Plant Ind. Bull. 196: (40 pp. ), 4 pis. 
1910. Dow, Geo., The Status of the "False " Wild Oats. Can. 

Seed-Grow. Assoc. Rep. 6: 105-107. 
1910. Drzewina, a.. La transmission des caracteres heredi- 

taires chez les hybrides. Revue des Idees, 7 : 372-376. 
1910. East, Edward M., ^ Mendelian Interpretation of Varia- 
tion that is apparently Continuous. Am, Nat. 44 : 65-82. 

7 tab. Bibliog. in notes. 
1910. East, Edward M., Inheritance in Potatoes. Am. Nat. 

44 : 424-430. Bibliog. in notes. 
1910. East, E. M., Notes on an Experiment concerning the 

Nature of Unit Characters. Science, n.s. 32 : 93-95. 
1910. East, E. M., The Role of Hybridization in Plant Breeding. 

Pop. Sci. Mo. 77 : 342-355, figs. 1-11. 
1910. East, E. M., The Transmission of Variations in the 

Potato in Asexual Reproduction. Conn. Agr. Exp. Sta. 

Rep. 119-160, 5 pis. Rev. in Zeitsch. f. indukt. Abst.- 

u.Vererb. 4:375-376. 
1910. Emerson, R. A., The Inheritance of Sizes and Shapes in 

Plants. Amer. Nat. 44:739-746. Rev. in Zeitsch. f. 

indukt. Abst.- u. Vererb. 5: 193. 
1910. Fletcher, S. W., Varieties of Fruit Originated in Mich. 

Mich. Agr. Exp. Sta. Spec. Bull. 44. 
1910. Frost, H. B., Variation as related to the Temperature 

Environment. A. B. A. Rep. 6: 384-396. 



368 Plant-Breeding 

1910. Frye, T. C, Height and Dominance of the Douglas Fir. 
Forest Quart. 8 : 465-470. 

1910. Gassner, G., tjber Solanum Commersonii und S. "Com- 
mersonii violet " in Uruguay. Landw. Jahrb. 1011-1020. 
1 pi. 

1910. Gates, R. R., Abnormalities in (Enothera. Missouri 
Bot. Gard. Ann. Rep. 21 : 175-184, pis. 29-31. 

1910. Gates, R. R., The Earliest Description of (Enothera 
Lamarckiana. Science, n.s. 31 : 425-426. 

1910. Gates, R. R., The Material Basis of Mendelian Phenom- 
ena. Am. Nat. 44 : 203-213. Bibliog., 1 p. 

1910. Gauss, Robert, Acclimatization in Breeding Drought- 
resistant Cereals. Am. Breed. Mag. 1 : 209-217. 

1910. Griffon, E., Sur la variation dans le greffage et V hybri- 
dation asexuelle. Acad. Sci., Paris, Comp. Rend. 150: 
629-632. 

1910. Griffon, E., Variations avec ou sans greffage chez les 
Solanees et les Composees. Soc. Bot, de France Bull. 57 : 
517-535, 2 pi. 

1910. Groff, H. H,, Hybridizing the Gladiolus. Are its Lessotis 
Possible of General Application? Can. Seed-Grow. Assoc. 
Rep. 6 : 52-58. 

1910. Guthrie, C. C, On Graft Hybrids. A. B. A. Rep. 6: 
356-373. 

1910. Haecker, Valentin, Die Radiolarien in der Variations- 
und Vererbungslehre. Zeitsch. f. indukt. Abs.- u. Vererb. 
2 : 1-17. Rev. in Arch. f. Entwick'mech. d. Org. 29 : 573. 

1910. Hansen, N. E., Is Acclimatization an Impossibility? 
N. Y. Hort. Soc. Mem. 2 : 69-74. 

1910. Harper, J. N., Experiments with Hybrid Cottons. South 
Carolina Agr. Exp. Sta. Bull. 148: (17 pp.). 

1910. Hartley, C. P., Seed Corn. U. S. Dept. Agr. Farmers' 
Bull. 415: (12 pp.), 3 figs. (This bulletin contains direc- 
tions for the growing, selection^ and care of seed corn. 



Appendix D 369 

the destruction of weevils or grain moths, the testing, 
grading, and shelhng of the corn to be planted, with sug- 
gestions to the corn grower as to the importance and re- 
quirements of good seed, and adaptability of any variety 
to his locality.) 
1910. Henry, A., On Elm Seedlings Showing Mendelian Results. 

Linn. Soc. Bot. Jour. 39 : 290-300. 
1910. Henslow, G., The Origin and History of our Garden 
Vegetables and their Dietetic Values — //. Royal Hort. Soc. 
Jour. 36 : 345-357, figs. 120-125. Roots and tubers. 
1910. Henslow, G., The Origin and Histonj of our Garden 

Vegetables. Roy. Hort. Soc. Jour. 36: 115-127. 
1910. Herre, a. C., Suggestions as to the Origin of California's 

Lichen Flora. Plant World, 13 : 215-220. 
1910. Heuer, W., Pfropfbastarde. Gartenflora, 59 : 434-438. 
1910. Himmelbaur, W., Der Gegenwdrtige Staiid der Pfropfhy- 

bridenfrage. Natw. Ver. Univ. Wien Mitt. 8 : 105-127. 
1910. Hindle, Edward, A Cytological Study of Artificial Par- 
thenogenesis in Strongylocentrotus Purpuratus. Arch. f. 
Entwick'mech. d. Org. 31 : 145-163, 1 pi. Bibliog. li pp. 
1910. Howard, Albert," and Howard, Gabrielle, Wheat 
in India. Its Production, Varieties, and Improvement. 
Calcutta. 288 pp., 7 maps, 4 figs., 7 pis. Rev. in Zeitsch. f. 
indukt. Abst.- u. Vererb. 4 : 153-154. 
1910. Humphreys, E. W., Variation among Non-lobed Sassafras 

Leaves. Torreya, 10 : 101-108, figs. 1-8. 
1910. HuRD, Wm. D., Corn Selection for Seed and for Show. 

Mass. State Board of Agr. Ann. Rep. 58. 
1910. Hurst, C. C., MendeVs Law of Heredity and its Applica- 
tion to Horticulture. Roy. Hort. Soc. Jour. 36 : 22-52. 
1910. Ikeno, J., Sind Alle Arten der Gattung Taraxacum 
Parthenogenetischf Deutsch. Bot. Gesell. Ber. 28-394- 
397. 

1910. Javillier, M., Sur la migration des alcaloides dans les 
2b 



370 Plant-Breeding 

greffes de Solanees sur Solonees. Inst. Pasteur Annales, 

24 : 569-576. 
1910. Kearney, Thomas H., Breeding New Types of Egyptian 

Cotton. U. S. Dept. Agr. Bur. Plant Ind. Bull. 200 : (39pp.) 

4 pi. 
1910. Keeble, Frederick, and (Miss) Pellew, C, The Mode 

of Inheritance of Stature and of Time of Flowering in Peas. 

Pisum sativum. Jour, of Gen. 1 : 47-56. 
1910. Keeble, Frederick, and (Miss) Pellew, C, White 

Flowered Vai^ieties of Primula sinensis. Jour, of Gen. 

1 : 1-5. 
1910. Keeble, F., Pellew, C., and Jones, W. N., The In- 
heritance of Peloria and Flower Colour in Foxgloves {Digi- 
talis purpurea). New Phytolog. 9 : 68-77, 1 fig. 
1910. Kroll, H. G., tjher Polygamic bei Polygonatum officinale. 

Bot. Ver. Brandenb. Verh. 52: 98^101. 
1910. Lecaillon, a., La parthenogenese naturelle rudimen- 

taire. Bull. Scientif . de France et Belgique, 7th ser. 44 : 

235-272. 
1910. Love, Harry H., Are Fluctuations Inherited? Am. Nat. 

44 : 412-423, 9 figs. & 4 tab. Bibliog. in notes. 
1910. MacDougal, D. T., Vail, A. M., and Shull, G. H., 

Mutations, Variations, and Relationships of the (Enotheras. 

Carnegie Inst. Wash. Publ. 81: (92 pp.) 1907. Rev. in 

Zeitsch. f. indukt. Abst.- u. Yererb. 3 : 226-228. 
1910. ]\Iaigre, E. F., Uheredite Mendelienne. Rev. des 

Idees, 234-242. 
1910. Moorehouse, L. A., Improvements of Bermuda Grass. 

Am. Breed. Mag. 1 : 95-98, fig. 
1910. Morgan, T. H., Chromosomes and Heredity. Am. Nat. 

44 : 449-496, 3 tab. lUus. 
1910. Nakano, H., Variation and Correlation in Rays and Disk 

of Aster fastigiatus. Bot. Gaz. 49 : 371-378, figs. 1-4. 
1910. Nash, G. V., Observations on Hardiness of Plants culti- 



Appendix D 371 

vated at the New York Botanical Garden. N. Y. Hort. 

Soc. Mem.2: 130-143. 
1910. Xemec, B., Das Problem der Befruchtungavorgdnge. 

526 pp. Borntraeger, Berlin. 5 pis. & 119 figs. 
1910. Newman, L. H., The Correlation of Characters in Plants 

and its Economic Importance to the Plant Breeders. Ottawa 

Nat. 23 : 220-224. 
1910. NiENBURG, W., Die Jungsten Ergebnisse der Pfropf- 

bastardforschung. Gartenflora, 59 : 479-495. 
1910. Nilsson-Ehle, H., Kreuzungsuntersuchungen an Hafer 

und Weizen. Lunds Universitats Areskirft. N. F. Afd. 

2. 5: 1-122. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 

3:290-291. 
1910. Nilsson-Ehle, H., Svalofs Pudelhvete. Sveriges Utsades- 

for. Tidskr. 20 : 69-87. 
1910. Oliver, George W., Neiv Methods of Plant Breeding. 

Fig. Am. Breed. Mag. 1 : 21-30. 
1910. Orchard, Harold, Potato Breeding in Manitoba and 

Some Results Obtained. Can. Seed-Grow. Assoc. Rep. 6 : 

103-104. 
1910. OsTENFELD, C. H., Further Studies on Apogamy and 

Hybridization of Hieracium. Zeitsch. f. Indukt. Abst. 3 : 

(Heft 4). Rev. in Am. Nat. 44:750-762. Bibliog. in 

notes. 
1910. Paton, Alkman, Notes on Some Hybrid Tuberous Solanums. 

Roy. Hort. Soc. Jour. 36: 127-133. 
1910. Pearl, Raymond, and Surface, F. M., Experiments in 

Breeding Sweet Corn. Maine Agr. Exp. Sta. Bull. 183 : 

(66 pp.). 
1910. Pearson, Karl, Darwinism, Biometry and Some Recent 

Biology, I. Biometrika, 7 : 368-385. Tab. 
1910. Pearson, Karl, On a New Method of Determining Cor- 
relation when one Variable is given by Alternative and the 

Other by Multiple Categories. Biometrika, 7 : 248-257, Tab, 



372 Pla7i t- Breeding 

1910. Planchon, Mutation gemmaire dii Solanum Conimersonii. 

Soc. Nation. d'Agr. Bull. 70 : 373-375. 
1910. Rehder, a., a New Hybrid Cornus {Cornus rugosa X 

stolonifera) . Rhodora, 12:121-124. C. Slavinii Rehder. 
1910. RiCHTER, 0., PJropfungen, Pfropfbastarde und Pflanzen- 

chimaeren. Lotos, 58: 1-22, 
1910. RiETz, H. L., Correlation in Corn. 111. Agr. Exp. Sta. 

Bull. 148: (25 pp.). 
1910. Salaman, R. N., The Inheritance of Colour and Other Char- 
acters in the Potato. Jour, of Gen. 1 : 7-46, 29 pi. Rev. 

in Zeitsch. f. indukt. Abst.- u. Vererb. 5 : 192-193. 
1910. Saunders, E. R., Studies in the Inheritance of Double- 

ness in Flowers. I. Petunia. Jour, of Gen. Fig. 1 : 57. 
1910. ScHRiBAux, Sur le Solanum Conmiersoiiii. Soc. Nation. 

d'Agr. Bull. 70:798-801. 
1910. Shepperd, J. H., Report of Co7nmittee on Breeding Fiber 

Crops. Am. Breed. Mag. 1 : 197-199. 
1910. Shoemaker, D. N., Report of Committee on Breeding 

Cotton. Am. Breed. Mag. 1 : 293-294. 
1910. Shull, George Harrison, Color Inheritance in Lychnis 

dioica L. Am. Nat. 44 : 83-91, 3 tab. Bibliog. 
1910. Shull, A. Franklin, The Artificial Production of the 

Parthenogenetic and Sexual Phases of the Life Cycle of Hyda- 

tina senta. Am. Nat. 44 : 146-150, 5 tab. 
1910. Shull, George Harrison, Hybridization Methods in 

Corn Breeding. Am. Breed. Mag. 1 : 98-107. Bibliog. 
1910. Smith, Louie H., Increasing Protein and Fat in Corn. 

Am. Breed. Mag. 1 : 15-21. Tab. 
1910. Smith, J. Russell, Breeding and Use of Tree Crops. 

Am. Breed. Mag. 1 : 86-91. 
1910. Spillman, W. J., A Theory of Mendelian Phenomena. 

Am. Breed. Mag. 1 : 113-125. Diagr. 
1910. Spillman, W. J., Effect of Recent Discoveries 07i the Art 

of Breeding. Am. Breed. Mag. 1 : 69-70. 



Appendix D 373 

1910. Spillman, W. J., Mendelian Phenomena without de 

Vriesian Theory. Am. Nat. 44 : 214^228, 4 tab. Bibliog. 

in notes. 
1910. Spillman, W. J. (Reviewer), Heredity. (Rev.) Am. 

Nat. 44 : 504-512. Bibliog. in notes. 
1910. Spillman, W. J., The Nature of "Unit'' Characters. 

The American Naturalist, 43 : 243-248. Rev. in Zeitsch. 

f. indukt. Abst.- u. Vererb. 3 : 110. 
1910. Stevens, R. L., and Hall, J. G., Variation of Fungi 

Due to Environment. Bot. Gaz. 48:1-30, fig. 37. Rev. 

in Zeitsch. f. indukt. Abst.- u. Vererb. 3 : 343-344. 
1910. SuDWORTH, George S., Report of Committee on Breeding 

Nut and Forest Trees. Am. Breed. Mag. 1 : 185-193. Tab. 
1910. Taylor, George M., The Cross Fertilization of the 

Potato. Gard. Chron. 3d ser. 48 : 279. 
1910. Tischler, G., Ujitersuchungen uber die Entwicklung des 

Bananen-P aliens. Arch. f. Zellforschung, 5 : 622-670, 2 pis. 

& 4 figs. 
1910. Trabut, L., Sur une mutation inerme du Cynana Cardun- 

culus. Soc. Bot. de France Bull. 57 : 350-354, 2 pis. 
1910. Tracy, W. W., Breeding and Raising Garden Seeds. 

Mass. State Board cf Agr. Ann. Rep. 58. 
1910. Tracy, W. W., Report of Committee on Breeding Vege- 
tables. Am. Breed. Mag. 1 : 110-113. 
1910. TuTTLE, A. H., Mitosis in (Edogonium. Jour. Fxp. 

Zool. 9: 143-157, 18 figs. 
1910. ViLMORiN, Philippe de, Recherches sur Vheredite men- 

delienne. Acad. Sci., Paris, Compt. Rend. 151 : 548-551. 
1910. Vries, H. de, The Production of Horticultural Varieties. 

Roy. Hort. Soc. Jour. 35 : 321-326. 
1910. Waldron, L. R., a Suggestion regarding Heavy and 

Light Seed Grain. Am. Nat. 44:48-56. 
1910. Waldron, L. R., Heredity in Popidations and in Pure 

Lines. Plant World, 13 : 1-12, figs. 1-5. 



374 Plant-Breeding 

1910. Westgate, J. M., Variegated Alfalfa. U. S. Dept. Agr. 

Bur. Plant Ind. Bull. 169 : (63 pp.), 9 pis. & 5 figs. 
1910. Wheeler, Seager, Plant Breeding of the Farm. Can. 

Seed-Grow. Assoc. Rep. 6: 107-109. 
1910. Wheldale, M., Plant Oxydases and the Chemical Inter- 
relationships of Colour-varieties. Prog. Rei. Bot. Vol. 

3 : 457-473. Bibliog. in notes. 
1910. Wilson, E. B., Studies on Chromosomes. Jour. Exp. 

Zool. 9 : 53-79. 
1910. Winkler, H., Uber das Wesender Pfropfbastarde. (Vor- 

Idufige Mitteilung.) Deutsch. Bot. Gesell. Ber. 28 : 116-118. 
1910. Winkler, H., Uber die Nachkommenschaft der Solanus- 

Pfropfbastarde und die Chromosomes zahlen ihre Keimzellen. 

Zeitschr. fiir Botanik. 2 : 1-33. Rev. in Zeitsch. f. indukt. 

Abst.- u. Vererb. 3:223-224. 
1910. Winkler, Hans, Weiters Mitteilungen ilber Pfropfbastarde. 

Zschr. f. Botanik. 1 : 315-345, 1 pL, 4 figs. Rev. in Zeitsch. 

f. indukt. Abst.- u. Vererb. 3: 111-113. 
1910. Winkler, Hans, Zur Kritik der Ansichten von der Ent- 

stegung der Angiospermenbluten. Schles. Ges. Vaterl. 

Kult. Bteslau. Jahresber. 87 : 22-28. 
1910. WiNSLOw, E. J., A New Hybrid Fern. Am. Fern Jour. 

1 : 22-23, figs. 1-4. 
1910. WiTTE, H., Vallvdxtfdrddlingen pa Svalof, dess nodvdndighet 

och behafver af utstrdckt inhemsk froodling . Sveriges Utsades- 

for. Tidskr. 20:317-331. 
1910. Zavitz, C. a., Heredity in Plants and its Bearing on Agri- 
cultural Problems. Can. Seed-Grow. Assoc. 6th Ann. 

Meeting Rep. 49-52. 

1910. Zeijlstra, H. H., On the Cause of Dimorphism in (E710- 
thera nanella. Kon. Akad. Wetensch. Amsterdam Proc. 
13 : 660, 1 pi. 

1911. Agee, Hamilton P., Propagation of Seedlings of Sugar 
Cane in Louisiana. A. B. A. Rep. 6: 178-183. 



Appendix D 375 

1911. Atkinson, Alfred, Grain Investigations with Different 
Varieties of Wheat, Oats, and Barley. (Types and variety 
tests.) Montana Agr. Exp. Sta. Bull. 84 : 24 pp. 

1911. Babcock, Ernest B., Walnut-Oak Hybrid Experiments. 
A. B. A. Rep. 6: 138^141. 

1911. Balls, W. Lawrence, The Inheritance of Measurable 
Characters in Hybrids between Reputed Species of Cotton. 
IV Inter. Conf. Genetique, Paris, 429-440, fig. 9. 

1911. Bally, W., Cytologische Studein an Chytridineen. Jahrb. 
wissensch. Bot. 50 : 95-156, 5 pis. & 8 figs. 

1911. Barrus, M. F., Variation of Varieties of Beans in their Sus- 
ceptibility to Anthracnose. Phytopathology, 1 : 190-195, 1 pi. 

1911. Bateson, W., and Punnett, R. C, Reduplication of 
Terms in Series of Gametes. IV Inter. Conf. Genet. Paris, 
99-100. 

1911. Bembower, W., Pollination Notes from the Cedar Point 
Region. Ohio Nat. 11 : 378-383. 

1911. Benedict, Ralph C., Do Ferns Hybridize ? Science, 
n.s. 33 : 254-255. 

1911. Bringham, E. S., a Yearns Work in Potato Breeding. 
R. N. Y. 70 : 559. 

1911. Blaringhem, L., L'etat present de la theorie de la mu- 
tation. Soc. Bot. de France Bull. 58 : 644-652. 

1911. Blaringhem, L., Sur Vheredite en Mosaique. IV Inter. 
Conf. Genet. Paris, 101-151. 

1911. Braem, F., Die Varoatio7i bei den Statoblasten von Pec- 
tinatella magnijica. Arch. f. Entwick'mech. d. Org. 32 : 
314-348, 8 figs., 2 tab. Bibliog. \ p. 

1911. BuFFUM, B. C, Effect of Environment on Plant Breeding. 
A. B. A. Rep. 6:212-225. 

1911. Campbell, Douglas Houghton, The Nature of Graft- 
Hybrids. Am. Nat. 45 : 41-53, 1 fig. Bibliog. in notes. 

1911. Chubbuck, Levi, A Variety of Corn for Elevated Regions. 
Am. Breed. Mag. 2:235, fig. 



376 Plant-Breeding 

1911. Clements, Frederick B., Proposals for a System of 

Tree Breeding. A. B. A. Rep. 6 : 275-282. 
1911. Clothier, Geo. T., Breeding to Improve Physical Qualities 

of Timber. A. B. A. Rep. 6 : 170-172. 
1911. Clute, W. N., and Ferriss, J. H., A New Species of 

Phlox. Am. Bot. 17 : 74-76. Phlox argillacea sp. nov. 
1911. Collins, G, N., and Kempton, J. H., Inheritance of 

Waxy Endosperm in Hybrids of Chinese Maize. IV Inter. 

Conf. Genet. Paris, 347-357. Tab. X. 
1911. Collins, G. N., Increased Yields of Corn from, Hybrid 

Seed. U. S. Dept. Agr. Yearbook, 319-328. 
1911. Cook, 0. F., Hindi Cotton in Egypt. U. S. Dept. Agr. 

Plant Ind. Bull. 210 : 1-58, pis. 1-6. 
1911. Cook, 0. F., and Meade, R. M., Arrangement of Parts 

in the Cotton Plant. U. S. Dept. Agr. Plant Ind. Bull. 

222 : 26, figs. 1-9. 
1911. CouPiN, H., Sur la localisation des pigments dans le 

tegument des graines de haricots. Acad. Sci. Compt. 

Rend. 153: 1489-1492. 
1911. Creed, Richard, The Growing of Turnip Seed in the 

Maritime Provinces. Can. Seed-Grow. Assoc. Rep. 7 : 

49-50. 
1911. Dallimore, W., Notes on Trees suitable for Experimental 

Forestry. Kew Bull. Misc. Inf. 1911 : 211-223. 
1911. Daniel, L., Etude biometrique de la descendance de 

Haricots greffes et de Haricots francs de pied. Acad. 

Sci. Compt. Rend. 152: 1018-1020. 
1911. Daniel, L., Recherches biometrique sur tin hybride de 

greffe entre poirier et Cognassier. Acad. Sci. Compt. 

Rend. 152: 1186-1188. 
1911. Davenport, E., ^'Domesticated Animals and Plants.^' 

Science, n.s. 34 : 715. 
1911. Davis, Bradley Moore, Genetical Studies on (Enothera. 

II. Some Hybrids of (Enothera biennis and 0. grandiflora 



Appendix D 377 

that resemble 0. Lamarckiana. Am. Nat. 45: 193-233, 18 

figs. Bibliog. f p. 
1911. Decker, H., MendeVs Law as Related to Heredity and 

Breeding. I-V. Horticulture, 13 : 635 ; 13 : 669 ; 13 : 705-706 ; 

13 : 741-742 ; 13 : 780. lUus. Translated from Cosmos by 

G. Thommen. 
1911. Delacroix, G., Maladies des plantes cultivees dans les 

pays chauds, publie par A. Maublanc, vol. 1., 605 pp. 

Challamel. Paris. 
1911. Emerson, R. A., Genetic Correlation and Spurious Allelo- 
morphism in Maize. Neb. Agr. Exp. Sta. Ann. Rep. 24 : 

59-90, 9 figs. 
1911. Emerson, R. A., Latent Colors in Corn. A. B. A. Rep. 

6 : 233-237. 
1911. Emerson, R. A., Production of a White Bean Lacking the 

Factor for Total Pigmentation. A Prophecy Fulfilled. 

A. B. A. Rep. 6:396-397. 
1911. Evans, G. W., Wheats and Wheat Breeding. Agr. Jour. 

of Brit. East Africa, 3 : 348-356. 
1911. EwiNG, E. C., Correlation of Characters in Corn. Cornell 

Univ. Agr. Exp. Sta. Bull. 287 : 67-100, 14 tab., 2 figs. 
1911. Fairchild, David, Plant Introduction for the Plant 

Breeder. U. S. Dept. Agr. Yearbook, 411-422, 6 pis. & 

1 fig. Same. Yearbook Separate, 580: 411-422, 6 pis. 
1911. FooTE, E. H., A Study of the Supposed Hybrid of the 

Black and Shingle Oaks. Sci. Lab. Denison Univ. Bull. 

16:315-338, pis. 11-14. 
1911. Freeman, E. M., Resistance and Immunity in Plant 

Diseases. Phytopathology, 1 : 109-115. (Also published 

in Publ. Bot. Soc. Am. 50: 17-26.) 
1911. Freeman, G. F., and Jones, D. F., Plant Breeding. 

Univ. Arizona Agr. Exp. Sta. Ann. Rep. 541-546. 
1911. Gates, R. R., Mutation in (Enothera. Am. Nat. 45: 

577-606. Bibliog. 



378 Plant-Breeding 

1911. Gates, R. R., Studies on the Variability and Hentability 

of Pigmentation in (Enothera. Zeitsch. f. indukt. Abst.- u. 

Vererb. 4 : 337-372, pi. & o figs. Bibliog. | p. 
1911. Gauss, Robert, Acclimatization in Breeding Drought- 
Resistant Cereals. A. B. A. Rep. 6 : 147-156. 
1911. Gauss, Robert, The Plant Breeding Problem. Am. Breed. 

Mag. 2:259-263. 
1911. Gautier, Armand, Sur le Principe de la coalescence des 

plasmus vivants et Vorigine des races et des especes. IV 

International Conf. Genetique, Paris, 79-90. 
1911. Gexty, C, Note sur deux Carduus hybrides. iMonde 

des Plantes, 14 : 26. 
1911. Gilbert, Arthur W., Suggestions for an Undergraduate 

Course in Plant Breeding. A. B. A Rep. 6:352-356. 
1911. Gilbert, Arthur W., Suggestive Laboratory Exercises 

for a Course in Plant Breeding. Am. Breed. Mag. 2 : 196- 

212, fig. Tab. Bibliog. in notes. 
1911. Granier, J., and Boule, L., Sur le phenomene de con- 

jugaison des chromosomes a le prophase de la premiere 

cinese reductrice {microsporogenese chez Endymion nutans 

Bum). Acad. Sci. Compt. Rend. 152:393-396. 
1911. Gregory, R. P., Experiments with Primula sinensis. 

Jour, of Gen. 1 : 73. Illus. 
1911. Gregory, R. P., On Gametic Coupling and Repulsion in 

Primula sinensis. Roy. Soc. London Proc. 84 : 12-15. 
1911. Griffon, E., Greffage et Hijbridation Asexuelle. IV 

Internat. Conf. Genetique, Paris, 164r-196, figs. 24. 
1911. Griffon, E., Observations et recherches experimentales sur 

la variation chez le mais. Soc. Bot. France BuU. 57 : 604- 

615. 
1911. Groth, H. a.. The Fi Heredity of Size, Shape, and Number 

in Tomato Leaves. I. Seedlings. N. J. Agr. Exp. Sta. 

Bull. 238 : 3-38, 5 figs. & 1 pi. 
1911. Groth, H. A., The Fi Heredity of Size, Shape, Number 



Appendix D 379 

in Tomato Leaves. Part II. Mature plants. New Jersey 
Exp. Sta. Bull. 239: 3-12, pi. 1-9. 
1911. Hagedoorn, a. L., Facteurs Genetiques et Facteurs du 
Milieu dans V amelioration et Vohtentian des races. IV 
Internat. Conf. Genetique, Paris, 132-135. 
1911. Halstead, B. D., Geometrical Figures in Plant Breeding. 

Am. Breed. Mag. 2:217-220, fig. 
1911. Haxsen, N. E., Some New Fruits. So. Dak. Agr. Exp 

Sta. Bull. 130 : 163-200, 1 fig. 
1911. Harris, J. Arthur, On the Formation of Correlation and 
Contingency Tables when the Number of Combinations is 
Large. Am. Nat. 45: 566-571, 2 tab. Bibliog. in notes. 
1911. Harris, J. Arthur, The Biometric Proof of the Pure Line 

Theory. Am. Nat. 45 : 346-363. Bibliog. in notes. 
1911. Harris, J. Arthur, The Measurement of Natural Selec- 
tion. Pop. Sci. Mo. 78 : 521-538, figs. 1-7. 
1911. Hartley, C. P., The Corn Breeder's Problems. Am 

Breed. Mag. 2 : 212-217. Diagr. 
1911. Hatai, Shinkishi, The Mendelian Ratio and Blended 

Inheritance. Am. Nat. 45 : 99-106. Bibliog. 
1911. Hayes, H. K., and East, E. M., Improvement in Corn. 

Conn. Agr. Exp. Sta. Bull. 168: 21, 4 pis. 
1911. Hayes, H. K., Inheritance in Corn. Conn. (State) 

Agr. Exp. Sta. Ann. Rep. 407-427. 
1911. Heckel, E., Sur les mutations gemmaires culturales 
du Solanum Maglia et sur les premiers resultats culturaux 
de ces mutations. Acad. Sci., Paris, Compt. Rend 153- 
417-420. 
1911. Henry, J. L., Results obtained through the Use of Hand 

Selected Seed. Can. Seed-Grow. Assoc. Rep. 7 : 79-80. 
1911. Hill, E. J., (Enothera Lamarckiana: its Early Cultiva- 
tion and Description. Bot. Gaz. 51 : 13&-140. 
1911. HiLLMAN, F. H., Testing Farm Seeds in the Home and 
in the Rural School. U. S. Dept. Agr. Farmers' Bull. 428: 



380 Plant-Breeding 

(47 pp.), 32 figs. (This bulletin describes the seed-trade 
condition, the seed used as adulterants, methods and ap- 
paratus used in making tests, etc.) 

1911. Honing, J. A., Die Doppelnatur der (Enothera Lamarck- 
iana. Zeitsch. f. indukt. Abst.- u. Vererb. 4:227-278, 
10 figs. Bibliog. in notes. 

1911. Hopkins, L. S., A New Variety of the Cinnamon Fern. 
Am. Fern Jour. 1 : 100-101. Osmunda cinnamomea auri- 
culata var. nov. described and illustrated. 

1911. Humbert, E. P., A Quantitative Study of Variation. 
Natural and Induced, in Pure Lines of Silene noctiflora, 
Zeitsch. f. indukt. Abst.- u. Vererb. 4 : 161-226, 12 figs. 
Bibliog. in notes. 

1911. Hurst, C. C, The Application of the Principles of Genetics 
to Some Practical Problems. IV Internat. Conf. Genetique, 
Paris, 210-221. 

1911. Hus, H., and Murdock, A. W., Inheritance of Fascia- 
tion in Zea Mays. Plant World, 14 : 88-96, 1 fig. 

1911. Jansonius, H. H., and Moll, J. W., Der anatomische 
Bau des Holzes der Pfropfhybrids Cytisus Adami und ihrer 
Compomenten. Rec. Trav. Bot. Neerland. 8 : 333-368. 

1911. Jennings, H. S., Computation of the Coefficient of Cor- 
relation. Am. Nat. 45 : 413. 

1911. Jennings, H. S., Pure Lines in the Study of Genetics in 
Lower Organism. Am. Nat. 45 : 79-89. Diagr. 

1911. Jesenka, F., Sur un hybride fertile entre Triticum 
sativum {Ble Mold-Squarehead) and Secale Cereale. {Seigle 
de Petkus.) IV Inter. Conf. Genetique, Paris, 501-511. 

1911. JoHANNSEN, W., Mutotions dans des lignees pures de 
haricots et discussion au subject de le mutation en general. 
IV Internat. Conf. Genetique, Paris, 160-163. 

1911. Kastle, J. H., and Haden, R. L., Color Changes in Blue 
Flowers of Wild Chicory (Cichorium intybus). Amer. 
Chem. Jour. 46:315-325. 



Appendix D 381 

1911. Keeble, F., and Pellew, C, The Mode of Inheritance 

of Stature and of Time of Flowering in Peas {Pisum sativum). 
f Jour, of Gen. 1 : 47-56. Rev. in Zeitsch. f. indukt. Abst.- 

u. Vererb. 5:331. 
1911. KiJCK, G., Eine Mutation der Kartoffelsorte Up to Date. 

Monatsh. f. Landw. 4 : 108-109. 
1911. Kroemer, K., Uber das " Mendeln " und seine Bedeutung 

fUr die gdrtnerische Pflanzenziichtung . Mollers Deutsche 

Gartner-Zeitung, 26 : 50-52. 
1911. Lacke, M., and Parr, A. E., The Problem of the Im- 
provement of Cotton in the United Provinces of Agra and 

Oudh. Agr. Jour. India, 6 : 1-13, 5 pi. 
1911. Lang, H., Technisches aus dem Gebiete der Futterpfianzen- 

ziichtung. IIlus. Landw. Zeitung, 704. 
1911. Leake, H. M., Studies in Indian Cotton. Jour, of Gen. 

1 : 205-272. Illus. 
1911. Leidigh, a. H., Methods for the Improvement of Sorghum. 

Am. Breed. Mag. 2 : 294-296. Port. 
1911. LoTSY, J. p.. Hybrids entre especes d' antirrhinum. IV 

Inter. Conf. Genetique, Paris, 416-428, figs. 9. 
1911. Love, Harry H., Studies of Variation in Plants. Cornell 

Univ. Agr. Exp. Sta. Bull. 297 : 593-677, 70 figs., 48 tab. 
1911. MacDougal, D. T. , Climatic Selection in a Hybrid Prog- 

eny Oak. Plant World, 14: 129-131, 1 fig. 
1911. Mason, Silas C., Drought Resistance of the Olive in the 

Southwestern States. U. S. Dept. Agr. Bur. Plant Ind. 

Bull. 192: (60 pp.), 6 pis. & 20 figs. 
1911. Mayer, A., Bemerkungen zu G. Lewitsky : Uber die 

Chondriosomen in pflanzlichen Zellen. Deutsch. Bot. 

Gesell. Ber. 29: 158-160. 
1911. Mendel, G., Versuche Uber Pjianzenhybriden. Heraus- 

gegeben von E. v. Tachermak. Ostwalds Klassiker der 

exakten Wissenschaften, No. 121, 2d ed. Leipzig, Engel- 

mann. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 182. 



382 Plant-Breeding 

1911. Montgomery, E. G., Correlation Studies in Corn. Ne- 
braska Agr. Exp. Sta. Ann. Rept. 24 : 109-158. 

1911. Montgomery, E. G., Note regarding Maize Flowers. 
Science, n.s. 33 : 435. 

1911. Montgomery, E. G., Perfect Flowers in Maize. Pop. 
Sci. Mo. 79 : 346-349, figs. 1-6. 

1911. Morehouse, L. A., hnprovement of Bermuda Grass. 
Figs. A. B. A. Rep. 6:60-63. 

1911. Muller, R., Mutationen bei Typhus- und Ruhrhacterian. 
Mutation als spezifischee Kulturmerkmal. Centralbl. f. 
Bacteriologie, 58 : 1 : 97-106, 2 pis. 

1911. Mundy, H. S., Maize Breeding and Seed Selection. Rho- 
desia Agr. Jour. 8 : 385^390. 

1911. Munson, T. v.. Single Character vs. Tout Ensemble Breed- 
ing in Grapes. A. B. A. Rep. 6 : 183-189. 

1911. Newman, H. H., Reply to E. Godlewski's " Bemerkungen 
zu der Arbeit von H. H. Newman: 'Further Studies of the 
Process of Heredity in Fundidus Hybrids.^ " Arch. f. 
Entwick'mech. d. Org. 32 : 472-476. Bibliog. in notes. 

1911. Newman, L. H., Plant Breeding in Sweden. Can. Seed- 
Grow. Assoc. Rep. 7 : 89-99, 4 tab. 

1911. Nilsson-Ehle, H., Mendelisme et Acclimatation. IV 
Internat. Conf. Genetique, Paris, 136-157. 

1911. Nilsson-Ehle, H., Svalofs Solhvete, Ny sort for sodra 
Sverige. Sveriges Utsddesfor. Tidskr. 21 : 123-126, 1 pi. 

1911. Nomblot, a., Recherches de varietes fruitier es nou- 
velles. IV Inter. Conf. Genetique, Paris, 464-468. 

1911. Oliver, George W., New Methods of Plant Breeding. 
A. B. A. Rep. 6: 11-20. Figs. 

1911. Orton, W. a.. Disease Resistance in Varieties of Potatoes. 
Indiana Acad. Sci. Proc. 219-221. 

1911. Orton, W. A., The Development of Disease Resistance 
Varieties of Plants. IV Internat. Conf. Genetique, Paris, 
247 : 265, figs. 9. 



Appendix D 383 

1911. Owen, E. J., Inheritance Studies with Beans. N. J. Agr 

Exp. Sta. Bot. Dept. Rep. 277-281, 1 pi. 
1911. Parde, L., Enquete sur Vacclimation des essences exo- 

tiques en France. Soc. Dendr. France Bull. 19 : 5-12. lUus. 
1911. Pearl, Raymond, Biometrics. Am. Nat. 45:319-320. 
1911. Pearl, Raymond, Biometric Arguments regarding the 

Genotype Concept. Am. Nat. 45 : 561-566. Bibliog. in 

notes. 

1911. Pearl, Raymond (Reviewer), Some Recent Studies rni 
Variation and Correlation in Agricultural Plants. (Review ) 
Am. Nat. 45 : 415-425. Bibliog. 1 p. 

1911. Pearl, R., The Personal Equation in Breeding Experi- 
ments involving Certain Characters of Maize Biol Bull 
21:339-366. 

1911. Pearson, Karl, On a Correction to be made to the Cor- 
relation Ration. Biometrika, 8 : 254-256, pi. 

1911. Pole-Evans, J. B., South African Cereal Rusts with Ob- 
servations on the Problem of Breeding Rust-resistant Wheats 
Jour. Agr. Sci. 4 : 95-104. 

1911. Redfield, R. L., Acquired Characters Defined Am 
Nat. 45 : 571-573. 

1911. Roberts, F. B., A Method of Corn Pollination. Am 
Breed. Mag. 2 : 54-60. Fig. 

1911. Roberts, Herbert F., Breeding for Type of Kernel in 
Wheat. A. B. A. Rep. 6: 142-147. Figs. 

1911. Rudolph, J., UAster cordifolius et ses varietes. Rev 
Hort. 83 : 325-327. 

1911. RuGG-GuNN, A., Sociological and Other Aspects of the 
Unit-Character Conception. IV Inter. Conf. Genet., Paris, 

1911. Salaman, R. N., Studies in Potato Breeding. IV Inter. 

Conf. Genetique, Paris, 373-376. 
1911. Saunders, Edith R., The Breeding of Double Flowers. 

IV Inter. Conf. Genetique, Paris, 397-405. 



384 Plant-Breeding 

1911. Saunders, Charles E., Production de varietes de hie 

de haute valeur boulougere. IV Inter. Conf. Genet., Paris, 

290-300. 
1911. Saunders, E. R., Oji Inheritance of a Mutation in the 

Common Foxglove {Digitalis purpurea). New Phytologist, 

10 : 49-63, 1 pi. & 12 figs. 
1911. Scudder, H., Similarity of Color in Bud and in Leaf. 

Rhodora, 13 : 86-87. 
1911. Shamel, a. D., a Study of the Improvemeiit of Citrus 

Fruits through Bud Selection. U. S. Dept. Agr. Plant Ind. 

Circ. 77 : 1-19, 5 figs. 
1911. Sherff, E. E., Tragopogon pratensis X porrifolius. 

Torreya, 11 : 14-15. 
1911. Shull, G. H., a Pure-Line Method in Corn Breeding. 

Amer. Breeders' Assoc. Rep. 5 : 51-59. Rev. in Zeitsch. 

f. indukt. Abst.- u. Vererb. 5 : 331-332. 
1911. Shull, G. H., Defective Inheritance-Ratios in Bursa 

Hybrids. Naturf. Vereins Briinn Verb. 49: (12 pp.), 6 

pis. 
1911. Shull, G. H., Hybridization Methods in Corn Breeding. 

A. B. A. Rep. 6:63-72, figs. 
1911. Shull, G. H., Reversible Sex-Mutants in Lychnis dioica. 

Bot. Gaz. 52 : 329-368, 15 figs. 
1911. Smith, Louie H., Increasing Protein and Fat in Corn. 

A. B. A. Rep. 6:5-11. 
1911. Smith, Russell J., Breeding and Use of Tree Crops. 

A. B. A. Rep. 6:51-56. 
1911. Spillman, W. J., Heredity. Am. Nat. 45: 60-64. 
1911. Strampelli, N., De V etude des characteres anormaux 

presentes par les plantules pour la recherche des varietes 

nouvelles. IV Internat. Conf. Genetique, Paris, 237-246, 

figs. 11. 
1911. Styan, K. E., Pollen Grains. Rev. in Am. Bot. 17:41- 

44. Originally published in Selbourne Magazine. 



Appendix D 385 

1911. Sutton, W., Compte Rendu. D'esperiences de Croise- 
ments faites entre le pois sauvage de Palestine and les pois 
de commerce dans le but de decouvris entre eux quelque 
trace d'identite specifique. IV Inter. Conf. Genetique, 
Paris, 558-567, figs. 4. 

1911. Taylor, G. M., Disease Resisting Potatoes. Gard. 
Chron., 3d ser. 49: 181. 

1911. Tedin, H., Ar skalhalten hos arter en sortegenskap? 
(With German r^sum^.) Sveriges Utsadesfor. Tidskr, 
21 : 72-77. 

1911. The Sugar-Beet Industry is based on Breeding. Am. 
Breed. Mag. 2 : 234. 

1911. Thoday, M. G., and Thoday, 0., On the Inheritance 
of the Yellow Tinge in Sweet Pea Colouring. Cambridge 
Phil. Soc. Proc. 16:71-84. 

1911. Thomas, Rose Haig, Nicotiana Crosses. IV Inter. 
Conf. Genetique, Paris, 453-461, figs. 6. 

1911. Tower, W. L., The Determination of Dominance and the 
Modification oj Behavior in Alternative {Mendelian) In- 
heritance, by Conditions Surrounding or Incident upon the 
Germ-Cells at the Time of Fertilization. Biol. Bull. 18 : 
(No. 6). Rev. (Ger.) in Arch. f. Entwick'mech. d. Org. 
31 : 345-348. 

1911. Tracy, W. W., Report of Comniittee on Breeding Vege- 
tables. A. B. A. Rep. 6 : 75-78. 

1911. TscHERMAK, Prof. Erich VON, Examcu de le theorie 
des facteurs par le recroisement methodique des hybrids. 
IV Internat. Conf. Genetique, Paris : 91-95. Tab. VIIIc. 

1911. ViLMORiN, p. DE, and Bateson, W., A Case of Gametic 
Coupling in Pisum. Roy. Soc. London Proc. B. 84: 9-11. 

1911. ViLMORiN, Philippe de, Fixite des races de Froment. 
IV Inter. Conf. Genetique, Paris, 512-516. Tab. 3. 

1911. ViLMORiN, Ph. de, Recherches sur Vheredite mendelienne. 

Acad. Sci. Compt. Rend., 548-551. 
2c 



386 Plant-Breeding 

1911. VoGLER, Die Variationen der Blattspreite bei Cybisulabur- 

num L. Bot. Zentralbl. Beih. 27 : 337-390. 
1911. Vries, Hugo de, Intracellular Pangenesis. Translated 

into English by C. Stuart Gager, Chicago. Open Court 

Publ. Compt. Rev. in Zeitsch. f. indukt. Abst.-u. Vererb. 

5:90. 
1911. Vries, H. de, tjher doppeltreziproke Bastarde von (Eno- 

thera biennis L. und 0. muricata L. Biol. Centralbl. 31 : 

97-104. 
1911. Waldron, L. R., Variegation of European Alfalfas. 

Science, n.s. 33 : 310-312. 
1911. Wheldale, M., On the Formation of Anthocyanin. Jour. 

of Gen. 1 : 133. 
1911. Wheldale, M., The Chemical Differentiation of Species. 

Biochemical Jour. 5 : 445-456. 
1911. WiTTMACK, L., Botanische Fragen in Beziehung zur 

Kartoffelzuchtung. lllus. Landw. Zeitung, 51 : 289. 
1911. Woodruff, Chas. E., Breeding for Color Adjustment, 

under Certain Climates. Am. Breed. Mag. 2 : 313-000. 
1911. Zavitz, C. a.. Report of Committee on Breeding Cereals. 

A. B. A. Rep. 6: 141-142. 

1911. Zeijlstra, H. H., CEnothera nanella de Vries, eine krank- 
hafte Pfianzenart. Biol. Centralbl. 31 : 129-138. 

1912. AcLOQUE, A., La genealogie du chrysantheme. Monde 
des Plantes, 14 : 27-28. 

1912. Ball, Carleton R., and Hastings, Stephen H., Grain- 
Sorghum Production in the San Antonio Region of Texas. 
U. S. Dept. Agr. Bur. Plant Ind. Bull. 237 : (30 pp.), 4 figs. 

1912. Batchelor, Leon D., Carnation Breeding. A. B. A. 
Rep. 7 : 199-205. 

1912. Baur, Erwin, Vererbungs- und Bastardierungeversuche 
mit Antirrhinum. II. Faktorenkoppelung. Zeitsch. f. in- 
dukt. Abst.- u. Vererb. 6: 201-216, 3 tab. Bibliog. in 
notes. 



Appendix D 387 

1912. Beach, S. A., and Maney, T. J., Mendelian Inheritance 

in Prunus Hybrids. A. B. A. Rep. 7 : 214-227, fig. 
1912. Beach, S. A., Report of the Committee on Breeding Tree 

and Vine Fruits. A. B. A. Rep. 7 : 213. 
1912. Belling, John, Breeding Experiments with Forage Plants 

in Florida. A. B. A. Rep. 8 : 438-440. 
1912. Belling, John, Selection in Pure Lines. Am. Breed. 

Mag. 3:311-312. 
1912. Blaringhem, L., Les problemes de biologic appliquee 

examines dans la quatrieme conference internationale de 

genetique. Revue Scientifique, 50 : 50 : 265-269. 
1912. Brainerd, E., Violet Hybrids between Species of the 

Palmata Group. Torrey Bot. Club Bull. 39: 85-97, 3 

pis. 
1912. Burtt-Davy, J., Observations on the Inheritance of Char- 
acters in Zea Mays. Roy. Soc. South Africa Trans. 2 : 

261-270. 
1912. Castle, W. E., The Inconstancy of Unit-Characters. 

Am. Nat. 46 : 352-362. 
1912. Christie, W., Untersuchungen iXber alte norwegische 

Hafersorten. Fiihlings landw. Zeitung : 297. 
1912. CocKERELL, T. D. A., The Red Sunflower. Pop. Sci. 

Mo. 80 : 373-382. Illus. 
1912. CocKERELL, T. D. A., The Word Genotype. Science, 

n.s. 35 : 304. 
1912. Collins, G. N., and Kempton, J. H., An Improved 

Method of Artificial Pollination in Corn. U. S. Dept. Agr. 

Bur. Plant Ind. Circ. 89: (7 pp.), 2 figs. 
1912. Collins, G. N., Improvements in Technique of Corn 

Breeding. A. B. A. Rep. 8 : 349-353. 
1912. Cook, 0. F., Results of Cotton Experiments in 1911. 

U. S. Dept. Agr. Bur. Plant Ind. Circ. 96 : (21 pp.). 
1912. Davis, Bradley Moore, Genetical Studies on (Enothera. 

Ill, Further Hybrids of (Enothera biennis and 0. grandiflora 



388 Plant-Breeding 

that resemble 0. Lamarckiana. Am. Nat. 46 : 377-427, 

15 figs. Bibliog. ^ p. 
1912. Dean, A., The Potato and Floral Sterility. Gard. Chron. 

3d ser. 51 : 13. 
1912. Derr, H. B., The Breeding of Winter Barleys. Am. 

Breed. Mag. 3: 103-113. 
1912. DiLLMAN, A. C, Breeding Alfalfa as a Dry-land Crop. 

A. B. A. Rep. 8:414-424. 
1912. DoNCASTER, L., Sex-limited Inheritance in Cats. Science, 

n.s. 36 : 144. 
1912. Dorset, M. J., Variation in the Floral Structures of Vitis. 

Torrey Bot. Club Bull. 39 : 37-52, 3 pi. 
1912. Dorset, M. J., Variation Studies of the Venation Angles 

and Leaf Dimensions in Vitis. A. B. A. Rep. 7 : 227-250, 

fig. 
1912. East, E. M., A Study of Hybrids between Nicotiana 

Bigelovii and N. quadrivalvis. Bot. Gaz. 53 : 243-248, 

4 figs. 
1912. East, E. M., and Hats, H. K., Inheritance in Maize. 

Conn. Agr. Exp. Sta. Bull. 167: (137 pp.), 25 pis. Rev. 

in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 193-196. 
1912. East, E. M., Inheritance of Color in the Aleurone Cells 

of Maize. Am. Nat. 46 : 363-365. 
1912. East, E. M., The Application of Biological Principles 

to Plant Breeding. In Heredity and Eugenics, pp. 113- 

138, fig. 
1912. East, E. M., The Mendelian Notation as a Description 

of Physiological Facts. Am. Nat. 46 : 633-655, 1 tab. 
1912. FiNLOW, R. S., and Burkill, J. H., The Inheritance of 

Red Colour and the Regidarity of Self-fertilization in Cor- 

chorus capsularis L., the Common Jute-plant. India Dept. 

Agr. Bot. Ser. Mem. 4 : 73-92. 
1912. Frost, H. B., The Origiri of an Early Variety of Matthiola 

by Mutation. A. B. A. Rep. 8 : 536-545. 



Appendix D 389 

1912. Funk, Eugene D., Ten Years of Corn Breeding. Am. 

Breed. Mag. 3 : 295-302, 4 figs. 
1912. Gates, R. R., Early Historico-botanical Records of the 

(Enotheras. Iowa Acad. Sci. Proc. 85-124, 6 pis. Rev. 

in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 285-287. 
1912. Gerner, W. W., Some Observations on Tobacco Breeding. 

A. B. A. Rep. 8 : 458-468, fig. 
1912. Gernert, Walter B., A New Subspecies of Zea Mays L. 

Am. Nat. 46 : 616-622, 3 figs. 
1912. Gernert, Walter B., Methods in the Artificial Pollina- 
tion of Corn. A. B. A. Rep. 8 : 353-367. 
1912. Gilbert, A. W., A Mendelian Study of Tomatoes. A. B. 

A. Rep. 7 : 169-188. 
1912. Gilbert, A. W., and Upton, G. B., An Algebra of Men- 

delism and its Application to a Mixed Hybrid Population. 

A. B. A. Rep. 7:312. 
1912. Gilbert, A. W., Present Status of Plant-breeding In- 
struction in the United States. A. B. A. Rep. 7:7-11. 
1912. Glawe, M., Timotheezuchtung in Amerika. Deutsch. 

Landwirtsch. Gesell. Mitt. 146. 
1912. 'Groth, B. H. a.. The F2 Heredity of Size, Shape, and 

Number in Tomato Fruits. N. J. Agr. Exp. Sta. Bull. 

242 : 3-39, 3 pi. 
1912. Hartley, C. P., Brown, E. B., Kyle, C. H., and Zook, 

L. L., Cross-breeding Corn. U. S. Dept. Agr. Bur. Plant 

Ind. Bull. 218: (72 pp.), 1 fig. 
1912. Hartley, C. P., Brown, E. B., Kyle, C. H., and Zook, 

L. L., Cross-breeding Corn. U. S. Dept. Agr. Plant Ind. 

Bull. 218 : 5-72. 
1912. Hartley, C. P., Productivity of Seed Corn as Influenced 

by Factors Other than Heredity. A. B. A. 'Rep. 8 : 335-338. 
1912. Hartley, C. P., The Seed-Corn Situation. U. S. Dept. 

Agr. Bur. Plant Ind. Circ. 95 : (13 pp.), 2 figs. 
1912. Hauman-Merck, L., Observations sur la pollination 



390 Plant-Breeding 

d'une Malpighiacee du genre Stigmaphijllon. Rec. Inst. 

Bot. Leo Errera, 9 : 21-28, 1 fig. 
1912. Hayes, H. K., Methods of Corn Breeding. Ani. Breed. 

Mag. 3 : 99-108, pi. Tab. Bibliog. 
1912. IL\YES, H. K., Correlation and Inheritance in Nicotiana 

Tabacum. Connecticut Agr. Exp. Sta. Bull. 171 : 3-45, 

5 pis. 
1912. Hedrick, U. p., and Wellington, R., An Experiment 

in Breeding Apples. N. Y. (Geneva) Agr. Exp. Sta. Bull. 

350. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 8 : 347. 
1912. Hill, Arthur W., The History of Primula obconica, 

Hance, under Cultivation, with Some Remarks on the History 

of Primula siiiensis Sab. Jour, of Gen. 2: 1-20, 2 pis. 

Bibliog. in notes. 
1912. HousER, True, Certain Results in Ohio Tobacco Breeding. 

A. B. A Rep. 8:468-479. 
1912. Hunt, B. W., Fig Breeding. Univ. Georgia Bull. 12: 

107-110. 
1912. Johnson, Roswell H., The Malthusian Principle and 

Natural Selection. Am. Nat. 46 : 372-376. 
1912. Jones, W. Xeilson, Species Hybrids of Digitalis. Jour. 

of Gen. 2 : 71-88, 3 pis., 45 figs. Bibliog. in notes. 
1912. IL\JANUS, BiRGER, Geuctische Studien an Beta. Zeitsch. 

f. indukt. Abst.- u. Vererb. 6 : 137-139. (Correction : 

p. 268), 9 pis., 2 figs., 5 tab. 
1912. Kellogg, Vernon Ly^vian, The Animals and Man. 

An elementary text-book of zoologj^ and human physiology. 

495 pp. Henry Holt & Co., N. Y. Rev. in Science, n.s. 

35:270-272. 
1912. Leake, H..M-, and Peyshad, R., Observations on Certain 

Extra-Indian Asiatic Cottons. India Dept. Agr. Mem. 4: 

93-112, 7 pis. 
1912. Leighty, Clyde E., Correlation of Characters in Oats 

with Special Reference to Breeding. A. B. A. Rep. 7 : 50-61, 



Appendix D 391 

1912. Lewis, C. I., The Teaching of Genetics. A. B. A. Rep. 

8:327-329. 
1912. Lock, R. H., Notes on Color Inheritance in Maize. Royal 

Bot. Gard. Peradeniya Abbls. 5: (part IV). Rev. in 

Zeitsch. f. indukt. Abst.- u. Vererb. 8 : 347-348. 
1912. Love, H. H., A Study of the Large and Small Grain Ques- 
tion. A. B. A. Rep. 7 : 109-118. 
1912. Love, H. H., Relation of Certain Ear Characters to Yield 

in Corn. A. B. A. Rep. 7 : 29-40. 
1912. Love, H. H., The Relation of Seed Ear Characters to 

Earliness in Corn. A. B. A. Rep. 8 : 330-335. 
1912. LuTZ, A. M., Triploid Mutants in (Enothera. BioL 

Centralb. 32 : 385-435, 7 figs. 
1912. Macoun, W. T., Apple Breeding in Canada. A. B. A. 

Rep. 8 : 479-488. 
1912. McLendon, C. a., Mendelian Inheritance in Cotton 

Hybrids. Georgia Exp. Sta. BuU. 99 : 143-228, 20 figs. 
1912. MoxTGOMERY, E. G., Wheat Breeding Experiments. 

Nebraska Agr. Exp. Sta. Bull. 125 : 5-16, 7 pi. 
1912. Moore, A. R., On Mendelian Dominance. Arch. f. 

Entwick'mech. d. Org. 34 : 168-175, 9 figs. Bibliog. in 

notes. 
1912. Muller, R., Bahterienmutationen. Zeitsch. f. indukt. 

Abst.-u. Vererb. 8 : 305-324. Bibliog. I p. 
1912. MuNSON, T. v.. Problems in Breeding Tree and Vine 

Fruits. A. B. A. Rep. 7 : 13-214. 
1912. Myers, Clyde H., Effect of Fertility upon Variation and 

Correlation in Wheat. A. B. A. Rep. 7 : 61-74. 
1912. Newman, L. H., Principles Recognized in the Breeding 

of Cereal Plants at Svalof, Sweden. A. B. A. Rep. 8 : 502-508. 
1912. Norton, J. B., Asparagus Breeding. A. B. A. Rep. 8: 

440-444. 
1912. Park, J. B., and Smith, L. H., Experiment on the Methods 

of Conducting Plot Tests. A. B. A. Rep. 8: 525-528. 



392 Plant-Breeding 

1912. Planchon, L., Solanuin Commersonii et Solarium tubero- 
sum. Soc. Bot. de France Bull. 59 : 70-77. 
1912. Ramaley, Francis, Mendelian Proportions and the In- 
crease of Recessives. Am. Nat. 46 : 344-351, 4 tab. Bibliog. 

in notes. 
1912. Roberts, H. F., Variation and Correlation in Wheat. 

A. B. A. Rep. 7 : 80-109, figs. 
1912. Shamel, a. D., Bud Selection as a Means of Improving 

Citrus arid Other Fruits. A. B. A. Rep. 8 : 497-502. 
1912. Shull, G. H., Defective Inheritance-ratios in Bursa 

Hybrids. Naturf . Vereines in Briinn. Verhandl. 49 : 

(12 pp.), 6 pis. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 

6 : 281-282. 
1912. Shull, G. H., "Genotypes;' "Biotijpes," "Pure Lines," 

and "Clones.'" Science, n.s. 35:27-29. Bibliog. in notes. 
1912. Shull, G. H., Hermaphrodite Females in Lychnis dioica. 

Science, n.s. 36 : 482-483. 
1912. Shull, G. H., '' Phenotype " and "Clone." Science, 

n.s. 35 : 182-183. 
1912. Shull, G. H., Reversible Sex-Mutants in Lychnis dioica. 

Bot. Gaz. 52 : (No. 5). Rev. in Zeitsch. f. indukt. Abst.- u. 

Vererb. 6 : 282-283. 
1912. Smith, F. W., The Application of Mendelian Principles 

to Sugar-cane Breeding. West Ind. Bull. 12 : 365-377. 
1912. Smith, L. H., Occurrence of Natural Hybrids in Wheat. 

A. B. A. Rep. 8:412-414. 
1912. Snow, E. C., The Application of the Correlation Coefficient 

to Mendelian Distributions. Biometrika, 8 : 420-424. Tab. 
1912. Spillman, W. J., Chromosomes m Wheat and Rye. Science, 

n. s. 35 : 104. 
1912. Stockberger, W. W., A Study of Individual Performance 

in Hops. A. B. A. Rep. 8 : 452-458. 
1912. Sudworth, Geo. B., Annual Report of Committee on 

Breeding Nut and Forest Trees. A. B. A. Rep. 7 : 250. 



Appendix D 393 

1912. Vries, Hugo de, and Bartlett, H. H., The Evening 
Primroses of Dixie Landing, Alabama. Science, n.s. 36: 
599-601. 

1912. Waldron, L. R., Breeding Certain Field-crop Plants in 
the Cold Northwest. A. B. A. Rep. 8:429-438. 

1912. Waldron, L. R., Hardiness in Successive Alfalfa Genera- 
tions. Am. Nat. 46 : 463-469, 2 tab. 

1912. Waldron, L. R., Influence of Variegation in Alfalfa 
upon Hardiness. A. B. A. Rep. 8:424-429. 

1912. Waldron, L. R., Value of Continuous Selection and its 
Bearing upon Hardiness in Winter Wheat. A. B. A. Rep. 
7:74-80. 

1912. Watts, Francis, Work with Seedling Sugar-canes in the 
British W. I. ayid British Guiana. A. B. A. Rep. 7 : 167-169. 

1912. Webber, H. J., Preliminary Notes on Pepper Hybrids. 

A. B. A. Rep. 7: 188-199, fig. 

1912. Webber, H. J., The Cornell Experiments in Breeding 

Timothy. Am. Breed. Mag. 3 : 85-99, tab., 4 pis. 
1912. Webber, H. J., The Effect of Research in Genetics on 

the Art of Breeding. Science, n.s. 35 : 597-609. 
1912. Webber, H. J., The Production of New and Improved 

Varieties of Timothy. Cornell Univ. Agr. Exp. Sta. Bull. 

313:339-381, 10 pi. 
1912. Wellington, R., Influence of Crossing in Increasing the 

Yield of the Tomato. N. Y. (Geneva) Agr. Exp. Sta. Bull. 

346 : 57-76. 
1912. Williams, C G., Variation in Pure Lines of Wheat. A. 

B. A. Rep. 8:409-412. 

1912. Winkler, Hans, Untersuchungen ilber Pfropfbastarde. 

Erster Teil : Die unmittelbare, gegenseitige Beeinflussung der 

Pfropfsymbionten. 186 p. Jena, Gustav Fischer. 2 Illus. 

Rev. in Zeitch. f. indukt. Abst.- u. Vererb. 7 : 77-80. 
1912. ZooK, L. I., Tests with First Generation Corn Crosses. 

A. B. A. Rep. 8 : 338-343. 



APPENDIX E 

LABORATORY EXERCISES 

The following laboratory exercises are intended to serve merely 
as suggestions. It is impossible and inadvisable to attempt to 
outline a rigid set of exercises for instructors to follow. It is 
the hope that these may serve as hints or type exercises, capable 
of all sorts of modification to suit conditions. An attempt has 
been made to avoid elaborate laboratory equipment which is 
expensive and unnecessary. The instructor should always aim 
to arrange laboratory practicums so that the student's inquisi- 
tive curiosity may be aroused and he may be induced to find 
out things for himself from the material with which he has to 
work. These exercises are not arranged with any particular 
order or sequence. The sequence will depend on the time of 
the year, material at hand, and so forth. The first group of 
exercises is of a general nature, and the exercises on corn, 
potatoes, and the cereals are grouped more or less together. 

We wish to acknowledge the assistance of Professor E. E, 
Barker in the preparation of these exercises, most of which 
have been successfully used by him with large classes. A few 
new ones have been added. 

Exercise 1 

Field Study of Variations by making an Herbarium of Variations 

Have each student collect, press, and mount fifty variations 

of plants. This is an excellent exercise, because it calls the 

394 



Appendix E 



395 




Fig. 104. — A specimen herbarium sheet, showing variation in the leaves 

of the mulberry. 



396 



Plant- Breeding 




Fig. 105. — A specimen herbarium sheets showing differences between two 
leaves of the horse-i-adish. 



Appendix E 397 

student's attention very effectively to the vast extent of varia- 
tion in wild and cultivated plants. Since variation is the basis 
of artificial selection as well as evolution in nature, it is highly 
important that considerable time and attention should be given 
to this study. 

Material. — A botanical collecting case, 20 blotters, 12 X 18 
inches ; 50 mounting sheets, 12 x 18 inches ; 50 labels, and glue. 

The accompanying photographs represent specimens treated 
as above (Figs. 104 to 107). The following directions may be 
given to each student : — 

Directions for collecting, pressing, and mounting an herbarium of 

variations 

1. Search for fluctuations, plateations, mutations, and bud- 
variations of plant characters which have been discussed in the 
lectures. 

2. Collect as nearly the whole plant as practicable. The 
size of the mounting sheets is 12 X 18 inches. When you collect 
your specimens plan upon this size of sheet, and arrange them 
accordingly when you are putting them into the blotters. 

3. Do not mount large, woody branches showing different 
degrees of thorniness, etc., upon the mounting sheets, but pre- 
serve them in bundles properly labeled. 

4. If you wish to show variations of berries, such as thorn- 
apples, etc., dry the fruits and fasten them to the mounting sheets 
by threads. 

5. Leave specimens in the blotters until they are thoroughly 
dry. If you do not have enough blotters, take out the speci- 
mens which have been in the blotters for a week or more, and 
put them between pieces of newspapers, under pressure, until 
they become thoroughly dry. Then dry your blotters near a 
radiator and put in the fresh material. 

6. After the specimens have become thoroughly dry, stick 
them to the mounting sheets, preferably with glue Put a small 



398 Plant-Breeding 



^f^U^n 



Fig. 106. — a specimen herbarium sheet, showing variation in leaves of 

the Persian lilac. 



Appendix E 399 

band of adhesive tissue over the larger stems. Arrange the 
specimens, if possible, so that you have at least one variation 
on a sheet. 

7. Put the label on the lower right-hand corner, leaving a 
small margin. Attach the label to the mounting sheet with 
glue or paste, putting it only on the left edge of the label, that 
is, do not cover the back of the label with paste or glue. 

Sample of Label 



HERBARIUM OF VARIATIONS 

DEPARTMENT OF PLANT-BREEDING. NEW YORK STATE 
COLLEGE OF AGRICULTURE 



Name 

Locality Date 

Habitat 

Description of variation 



Class of variation 

Collector No. 



8. Before the specimen is handed in, fill in as many of the 
blank spaces on the label as possible. Place your name after 
the word "Collector." Fill in both the scientific and common 
names. 

9. Absolute neatness is essential. 

Exercise 2 

The Statistical Study of Type and Variability 

Making measurements. — The value and uses of the statistical 
method of studying variation are explained in Chapter IV. In 
dealing statistically with a group of organisms, or parts of them, 
the first step in the procedure is, of course, to collect data. These 



400 



Plant-Breeding 




Fig. 107. — A specimen herbarium sheet, sho^vdng variations in leaves 

of the blackberry. 



Appendix E 401 

will consist of quantitative measurements of characters to be 
studied. These data are later analyzed, certain constants are 
derived therefrom, and, lastly, the constants are interpreted. 
The conclusions of the breeder or the investigator are based on 
his interpretations of these constants. The meaning of the 
various constants is explained in Chapter IV. 

In coUecting data, it is important that as large a proportion 
as possible of the entire population should be measured. Fail- 
ing this, the sample should be fairly representative of the whole. 
The time or season during which measurements are taken is 
important where populations are to be compared. It would 
obviously be unfair to collect data one year on fully matured 
plants and another year on immatured plants. It is not always 
easy to avoid a selection, conscious or unconscious, but the 
collector should try to take his data with absolute impartiality. 
He should collect at random until he has obtained a represent- 
ative sample. Much time and labor will be saved if he can 
conveniently limit the number of individuals measured to a num- 
ber whose square root is an integer. 

^ The frequency distribution. — Having measured a representa- 
tive sample of the entire population, the next step is to sort the 
data. All individuals of the same or nearly the same size are 
grouped together in one order of magnitude. In order to give 
a clear understanding of what follows, let us take, for example, 
the data collected by a class of students on 500 bean plants! 
The individual lengths range from 5 cm. to 95 cm. This is 
known as the range of variability and the way in which the in- 
dividuals are distributed along the successive equal intervals in 
this range is spoken of as the frequency distribution of the vary- 
ing character. For convenience, these lengths may be grouped 
into classes, thus : 5-14; 15-24; 25-34 . . . 85-94. 

It is desirable that the number of classes be limited to not 
more than about a dozen, and thus the size of the class will 
depend upon the nature of the material. For example bean 
2d 



402 Plant-Breeding 

plants may vary in height from 5 cm. to 95 cm. ; to make the 
classes differ by only 1 cm. would give us 90 classes, which 
would be very inconvenient to handle mathematically. 

The class limits should be given in all cases, not the mid- 
point of the class. The magnitude of a class is its value and is 
designated by the sjonbol T"^. In calculations the mid-point of 
a class is used as the class value. The number of individuals 
falling into each class is termed its frequency and is symbolized 
b}" the letter /. The accompanying table shows how the various 
bean lengths are distributed throughout the range : — 

V f 

5-14 4 

15-24 72 

25-34 169 

35-44 125 

45-54 64 

55-64 38 

65-74 11 

75-84 11 

85-94 6 



500 



The graph or frequency polygon. — It is often desirable to 
present the data in a graphic way so that the eye can take in at 
a glance such information as would otherwise require an extended 
and careful study of quantities of figures. For this purpose the 
frequency polygon is used. Such a simple diagram or chart 
presents a picture embodying the chief characteristics of the 
given population. Its significance is apparent to the student at 
once. The frequency polygon is made, as explained in Chapter 
IV, by plotting the class range along the base-line or axis of 
abscissas. On the vertical axis, or axis of ordinates, are plotted 
the class frequencies. 

When all the frequencies have been plotted in their proper 
places on the chart they may be connected by a continuous 



Appendix E 403 

line. This will form the frequency or distribution curve, knowii 
also as the ^'probability curve." It will take the form of a 
Quetelet curve rising from the lowest class value at the left end 
of the base-line to an apex at the class of greatest frequency, 
then dropping to the right end at the highest class value. Such 
a curve shows at once four things about our data: (1) The 
extreme values, or the extent of the range, (2) the way in which 
the individuals are distributed throughout this range, (3) the 
prevailing type, or class of greatest frequency, and (4)' whether 
the curve is symmetrical, following the normal probability curve 
or not. If the classes are arranged along the base-line"^ in the 
sequence of their values instead of their frequencies, the curve 
wiU ascend constantly from the lowest value on the left end to- 
ward the highest value at the right end. This forms a Gallon 
curve. The Galton type of curve shows merely a different 
method of exhibiting the frequency distribution of a population 
that is under study. 

Mode.~T\\e class of greatest frequency, the most "popular " 
or ''modish" class, so to speak, is known as the mode or modal 
class. In our problem, the modal class is 25-34, or the mode is 
29.5, the mid-value of this class. This is oneway, and an excel- 
lent one, of expressing type. A tjijical bean plant of this popu- 
lation, we can say, is 29.5 cm. long. 

Modal coefficient. — It is desirable to know what proportion 
of the population conforms to this tj^pe, or falls into this modal 
class. This proportion, which is expressed as a percentage des- 
ignated as the modal coefficient, is found by dividing the number 
of individuals in the modal class by the total number of indi- 
viduals measured. In our example, it would be iff = .3836 = 
38.36 %, which is the percentage of the population in the class 
of greatest frequency, hence, the modal coefficient. 

Mean. — If one desires to know what an average individual 
in the population is worth, the mean, sjnibolized by the letter 
M, will show it. The mean shows the average value of the' 



404 Plant-Breeding 

population, hence it is only another method of expressing type. 
It 'is found by multiplying the mid-value of each class {V) by 
the number of individuals in that class (/), then summing the 
products and dividing this sum by the total number of individ- 

uals. The formula for this operation is •' ^ 

Thus : — 







^f — 




n 


V 




/ 




Vf 


9.5 


X 


4 


= 


38.0 


19.5 


X 


72 


= 


1404.0 


29.5 


X 


169 


= 


4985.5 


39.5 


X 


125 


= 


4937.5 


49.5 


X 


64 


= 


3168.0 


59.5 


X 


38 


— 


2261.0 


69.5 


X 


11 


= 


764.5 


79.5 


X 


11 


= 


874.5 


89.5 


X 


6 
500 


— 


537.0 
18970.0 


189 


70.0 


= 37.94 


cm. 



500 

We would get exacth^ the same result if we arranged the bean 
plants, in order of size, in a single line, placing them end to end, 
and then divided the total length of this line by 500, the number 
of individuals in it. 

Average deviation. — One way of expressing variability is to 
find out by how much, on the average, any individual in the 
population deviates from the mean, the constant thus secured 
being termed the average deviation. This is ascertained as 
follows : the amount by which each class differs from the mean, 
or in other words, the deviation from the mean (designated by 
D) is multiplied by the frequency of the corresponding class, 
and then 'the sum of these products is divided by the total 

1 The Greek letter capital "sigma" (S) indicates that the suru of 
a series of values is to be taken. 

The total number of individuals measured is designated by n. 



Appendix E 405 



Ul lllU 


IVIU 


ua,ib. 


XliL' 


luniiuia lur ine op 


ieraiion is ^ 

n 


our problem it \a 


ould be found as shown 


in the table : — 


V 




/ 




D 


Dj 


9.5 


X 


4 




28.44 


113.76 


19.5 


X 


72 




18.44 


1327.68 


29.5 


X 


169 




8.44 


1426.36 


39.5 


X 


125 




1.56 


195.00 


49.5 


X 


64 




11.56 


739.84 


59.5 


X 


38 




21.56 


819.28 


69.5 


X 


11 




31.56 


347.16 


79.5 


X 


11 




41.56 


457.16 


89.5 


X 


6 




51.56 


309.36 
5735.60 






5735.60 


= 11.4712 cm. 





500 



Of course, the deviations below the mean (28.44, 18.44, 8.44) 
are negative quantities, those above (1.56, 11.56, 21.56, 31.56, 
41.56, 51.56) positive, but inasmuch as we are here concerned 
only with deviation from type, we are correct in neglecting these 
signs, and using the arithmetic sum, and not the algebraic. 

We would secure the same result if we went along our line 
of bean plants spoken of above with an average or mean indi- 
vidual as a measure, added up the lengths by which each one 
missed of being an average individual, and then divided this 
total by 500, the number of individuals measured. Clearly this 
would give the amount by which, on the average, each individual 
missed of being the mean or the average individual. 

Standard deviation. — Another constant expressing departure 
from type, and one which is preferred by biometricians on mathe- 
matical grounds, is standard deviation, designated by the Greek 
letter small ''sigma " (o-). It is found by squaring the deviations 
from the mean before multiplying by the frequencies, dividing 
the summation of these products by the number of individuals, 



406 



Plant- Breeding 



and then extracting the square root of the quotient. The 
formula is : — 











m 












cr 


= \ n' 






V 


/ 


Vf 


D 


Df 


D2 


2)2/ 


5-14 


4 


38.0 


28.44 


113.76 


808.8336 


3235.3344 


15-24 


72 


1404.0 


18.44 


1327.68 


340.0336 


24482.4192 


25-34 


169 


4985.5 


8.44 


1426.36 


71.2336 


12038.4784 


35-44 


125 


4937.5 


1.56 


195.00 


2.4336 


304.2000 


45-54 


64 


3168.0 


11.56 


739.84 


133.6336 


8552.5504 


55-64 


38 


2261.0 


21.56 


819.28 


464.8336 


17663.6768 


65-74 


11 


764.5 


31.56 


347.16 


996.0336 


10956.3696 


75-84 


11 


874.5 


41.56 


457.16 


1727.2336 


18999.5696 


85-94 


6 


537.0 


51.56 


309.36 


2658.4336 


15950.6016 




500 


18970.0 




5735.60 




112183.2000 


M = 


= 37.94 


cm. 










Av. 


Dev. = 


= 11.4712 


! cm. 








(T = 


14.9789 cm. 











Performing the operations indicated by this formula, we find 
the standard deviation in our problem to be 



112183.2000 
500 



14.9789 cm. 



The squaring of the deviations has the effect of exaggerating 
the departures of the extremes, and thus the standard deviation 
is always greater than the average deviation, so that the two 
are not comparable. For the practical breeder the one is just 
as good as the other and whether he employs the average devia- 
tion or the standard deviation is of little practical importance 
so long as he is consistent in the use of one to the total exclu- 
sion of the other in the same piece of work. 

Finding the mean and the standard deviation by the " short 
method^ — Where large numbers are used, the derivation of the 
mean and the standard deviation by the method presented 



Appendix E 



407 



above is a long and laborious process, in which the liability to 
error is great. A much shorter, simpler, and at the same time 
more accurate method has been devised. This consists in mak- 
ing a guess at the mean (designated by G), and indicating the 
difference between each class value and this guess in a column 
marked {V-G). Each of these differences is then multiplied by 
the corresponding frequency and the algebraic sum of the total 
negative differences and the total positive differences is found. 
This is the total amount by which our guess missed the mean 
for the whole population, and hence we should divide this 
quantity by n to find the average amount by which we missed 
our guess. If this amount, which is called the '^correction," is 
positive, then our guess has been too low by that amount, and it 
is to be added to the guess. On the other hand, if it is negative, 
then our guess has been too high, and it is to be diminished by 
this amount. The formula for this procedure is : — 



correction (c) = (Algebraic) —^^^^ ^ 

M =G±c. 



n 



Length of Plants (Short Method) 



V 


/ 


(V-G) 


KV-G) 




/(F-G)2 


5-14 


4 


-30 


- 120 




3600 


15-24 


72 


-20 


1440 




28800 


25-34 


169 


-10 


-1690 


-3250 


16900 


35-44 


125 













45-54 


64 


10 


640 




6400 


55-64 


38 


20 


760 




15200 


65-74 


11 


30 


330 




9900 


75-84 


11 


40 


440 




17600 


85-94 


6 


50 


300 


2470 


15000 




500 




Sum 


= -780 


113400 


c =- 


- 780 


1.56 


c2 


= 2.4336 





500 



408 Plant-Breeding 

M= 39.5- 1.56 = 37.94 cm. 



o- =^^1^00 _ 2.4336 = V224.3664 = 14.9789 cm. 

C= 1M785 ^ 39.48%. 
37.94 

In our problem, the mean as determined by this method, as 
shown in the accompanying table, is exactly the same as was 
found by the long method, 37.94 cm. 

We would have secured the same result if, after a casual in- 
spection of the line of bean plants spoken of above, we guessed 
that the mean was 39.5, and taking an individual of this length 
as a measure, we found the total amount which the short ones 
lack of being equal in length to the assumed mean, or the guess, 
and likewise the total amount which the long ones exceed the 
guess. The algebraic sum of these two amounts would be the 
total amount by which our guess missed of being the true mean, 
and since 500 individuals were measured, the average amount 
by which we missed on each individual would be found by 
dividing this sum by 500. Our assumed length would then 
be corrected by this amount, just as above. If we had guessed 
that the mean was 37.94, and went through the same process, 
then the sum of the negative differences would have exactly 
counterbalanced the sum of the positive differences, since our 
guess in this case coincides with the true mean. 

It would have made no difference whatever had we made our 
guess at 9.5. Indeed, this would have the advantage that 
minus signs would be eliminated and thus a frequent source of 
error removed, since students are prone to forget the algebraic 
signs. On the other hand, larger numbers would be involved. 

In finding the standard deviation by the short method, the 
elements of the (V-G) column are squared before multiplying 
by the corresponding class frequencies. The sum of these prod- 



Appendix E 409 

ducts is then divided by n, just as in the long method. In find- 
ing the mean a certain correction was appUed to the guess. 
Now, since we are here dealing with squares, we must apply as 
a correction the square of the correction found previously ; but 
unlike the previous procedure, this square of the correction is 
always subtracted from the quotient found as stated above. 
(All this has been proven mathematically correct, but the proof 
is beyond the scope of this study.) The square root is then found 
as before. The fonnula for deriving the standard deviation by 
this method is : — 



• -4 



n 



Using this method, we find the standard deviation to be 
exactly the same as before, as shown in the table above and the 



following calculations : — 



^ =\/^^i^- (- 1-56)^ = 14.9789 cm. 

A further considerable shortening of the short method can be 
employed when the class values differ by amounts other than 
unity or a simple multiple of it, such as 10. In such a case 
the class differences arc to be treated as unity and a correction 
made at the end of the calculation. The modified formulae are : — 



M = G ± (ex True Difference between Classes) , 

X True Difference. 



V 



f{V-GY 
n 



The short method, because of its simplicity and its labor- 
saving features, recommends itself for general use. It is also 
slightly more accurate than the long method because no deci- 
mals are dropped until the very end of the calculation. 

Coefficient of variability. — Standard deviation, as a measure 



410 Plant-Breeding 

of variability, allows of comparison only between similar organ- 
isms or parts, between such characters as are measured in the 
same denomination, as tubers with tubers, or height measured 
in inches with height in inches. This is because it is not an 
absolute, or abstract constant, but really represents a certain 
number of feet, pounds, centimeters, or what not. And just as 
we cannot compare 5 pounds with 5 inches mathematically, so 
we cannot compare standard deviation in inches with that in 
pounds. 

An undenominational abstract constant that will allow of com- 
paring diverse variabilities, let us say, height with thickness, or 
pounds with inches, is designated as the coefficient of variability. 
It is found by dividing the standard deviation by the mean. 

The formula is — X 100 and it is symbolized by C. It is really 

only the standard deviation measured in terms of the mean. For 
our beans the coefficient of variability for length is .3948 or since 
it is usually read as percentage, 39.48 %. This constant is now 
comparable with any other coefficient of variability for what- 
ever character or in whatever denomination it may have been 
measured. Thus we can compare the variability in the length 
of beans in millimeters with their variability in breadth meas- 
ured in millimeters or inches, or with height in men or sugar 
content in beets, if we wish. 

Probable error. — Probable error does not mean the amount 
of error that an investigator is likely to make in his experiments 
or measurements. It means that if he would measure another 
random sample of a population similar in size and character to 
the sample he had measured before, the chances are even that 
the mean for the new sample would lie somewhere between the 
limits denoted by the probable error. Thus, the mean as to 
length of plants for our beans is 37.94 cm. with a probable error 
of ± .4518. This means that the mean for the new population 
would not be greater than 37.9400 + .4518 = 38.3918 cm., or 



Appendix E 411 

less than 37.94 - .4518 = 37.4882 cm., but would fall some- 
where in between these two Umiting values. It is sjrmbolized 
by E with the initial of the constant to which it belongs attached 
in smaller case type. Thus, the symbol for the probable error 
of the standard deviation is E^; of the mean, Em', of the co- 
efficient of variability, Ec. 

The probable errors are based upon certain relations between 
the standard deviation and the number of individuals. The 
greater the number of individuals, the smaller will be the prob- 
able error. In short, the probable error will indicate how much 
confidence we can place in our constant, and should always 
accompany the latter. It is really a part of the constant. 

In finding the probable errors the constant .6745 is used. 
This has been derived mathematically and is used by all biom- 
etricians in the same way. 

The following formulae will show how the various probable 
errors can be found : — 

^^ = ±.6745^. 

J^<.=±.6745-^. 

V2n 



Ec = 



C 
± .6745—:=, where C is 10 % or less.^ 



V2 



n 



V2n>' Vioo; 



± .6745 — =\ 1 + 2 -^^ ), where C is greater than 10 %.' 



Our completed constants for length of bean plants are then 
as follows : — 

M = 37.9400 ± .4518 cm. 

o- = 14.9789 ± .3195 cm. 

C = 39.48 ± .96 %. 

^ In these equations the value of C in per cent is to be used. The prob- 
able error will come out as a percentage. 



412 Plant-Breeding 

In the accompanying table the constants for the number of 
pods borne on these plants are likewise determined by the short 
method. Note that the colmnn {V-GY is entirely omitted, a 
short cut which is another considerable time saver. Instead, 
the elements of column /( V-G) are simply multiplied by the cor- 
responding elements of the {V~G) column since J{V-G) times 
{V-G) equals /(F-G)2. 

Number of Pods (Short Method) v 

V f (V-G) f{V-G) j{V-GY 

5-14 16 -20 - 320 6400 

15-24 140 -10 -1400 -1720 14000 

25-34 169 

35-44 115 10 

45-54 40 20 

55-64 12 30 

65-74 5 40 

75-84 ^ 50 

500 Sum = 940 74200 

c =^= 1.88 c2 = 3.5344 

500 

Mode = 29.5 Modal Coefficient = 38.36 % 

M = 29.5 + 1.88 = 31.38 ± .3631 (pods). 










1150 




11500 


800 




16000 


360 




10800 


200 




8000 


150 


+ 2660 


7500 



.-V 



74200 _ 3^3^^ ^ 12.0360 ± .2568 (pods). 
500 ^ ^ 



C = IM^ep ^ 3g3g ^ 33 3g g3 ^ 
31.38 



Exercise 3 
Correlation 



Certain characters in organisms tend to appear together 
and the inference is that they are causally connected, that is, 



Appendix E 413 

one is the cause of the other or else both are dependent upon 
the same cause. 

Two phenomena are causally connected if any one of the 
following four cases is true : — 

(1) If, when the first is present, the second is invariably present 
also. 

(2) If, when the first increases in amount, the second also in- 
variably increases a proportional amount. 

(3) If, when the first is absent, the second is invariably absent 
also. 

(4) If, when the first decreases in amount, the second also 
invariably decreases a proportional amount. 

Because a fixed or absolute relationship exists in each of the 
four cases the correlation between the two phenomena is said 
to be perfect, but in the first two cases it is positive in nature, 
in the second two negative in nature. If absolutely no relation 
existed between the two phenomena, the correlation would be 
zero. 

Now, in the bean problem used in the preceding exercise, it 
might be asked, ''Is there any fixed relation between the length 
of plant and its number of pods?" Suppose, for example, that 
if on selecting a plant from the whole lot, it was found to be a 
long one, could we then say, on this information only, that it will 
be found to bear a great number of pods? If so, we are assum- 
ing that some relation exists between the two characters. 

Let us, for the sake of illustration, suppose that each bean 
plant bears one pod for every centimeter in length. Because in 
this case there exists a fixed or absolute relationship, the corre- 
lation is said to be perfect, and is expressed by 100 %, or more 
usually simply by unity (1). 

Now, suppose, however, that on selecting 300 plants averag- 
ing 80 cm. in length, we find the first 100 plants to bear an 
average of 50 pods per plant, the second 25 pods, and the third 
10, it is clear that if we select one more plant at random and 



414 Plant-Breeding 

measure it to be 80 cm. also, we could no more predict the 
number of pods it bears than if we had not. measured it at all. 
Here, then, we say there is no relationship whatever between 
length of plant and number of pods, or, in other words, the cor- 
relation is 0. 

Now suppose a third case, in which we ,find that invariably 
the longest plant bears the fewest pods, and the shortest the 
most. Here we could say the relationship is fixed or absolute 
too, but in an opposite, or negative manner, and accordingly, 
the correlation would be expressed by — 1. 

But now turning back to the first supposition, where it was 
assumed that one pod was borne for each centimeter length, 
suppose that the relationship were not so definite. Suppose 
that one pod occurs not for every centimeter, but sometimes for 
a little more than a centimeter, sometimes for a little less ; then 
the relationship, though not absolute, is high, and the degree 
to which this relationship approaches the perfect 100 % relation- 
ship will express the correlation between the two characters. 
The correlation coefficient, in other words, would fall between 
and + 1. 

We rarely find characters or organs in an organism to be 
absolutely related; usually they are associated in a more or 
less intermediate degree, somewhere between and + 1, or 
and — 1. The degree to which they are associated, or corre- 
lated, if it can be determined in an exact manner and expressed 
by a mathematical constant, should be an index of the degree 
for which one is the cause of the other, or the probability of 
finding the other when we know the first is present. This may 
be of importance sometimes to the breeder because some easily 
seen character may be responsible for, or indicative of, the 
presence of a desired, but unseen character. Thus a certain 
shaped kernel of corn (one with a large germ) is known to run 
high in oil content, one with large endosperm high in starch. 
To select kernels with large germs is much easier than to analyze 



Appendix E 



415 



many ears by chemical methods. Or if, after a relation had 
been established, we could safely choose the longest or tallest 
bean plants right in the field and know that they will bear the 
greatest number of pods, it would be of great advantage to the 
breeder. 

Now, an exact determination of the degree of correlation can 
be obtained by the biometrical method. Let us follow the pro- 
cess step by step, using our bean data. 

First of all, we take our data for the two characters for which 
we wish to find the correlation, length of plant, and number of 
pods. 

Our original observations will be somewhat as follows : — 



No. OF Observation 
(or Plant) 


Length of Plant in Cm. 


No. of Pods 


1 

2 
3 

etc. 


27 
46 

18 
etc. 


32 

27 
45 

etc. 



In finding the constants — mean, standard deviation, etc., for 
each of these characters, the observations for length and those 
for number of pods were distributed in separate tables. Now, 
however, we distribute both sets of observations on one table, 
in what are known as arrays of a correlation table. (See Table 
1.) For example, the first observation tabulated above would 
fall in the vertical array 25-34, as regards length, and in the 
25-34 horizontal array, as regards number of pods. The second 
observation would fall in the 5th column (vertical array 45-54) 
and in the third row (horizontal array 25-34). 

Thus each vertical array would be a frequency distribution 
of length of plant with respect to number of pods, and each 



'416 Plant-Breeding 

horizontal array would be a distribution of number of pods 
with respect to length of plant. But if we add up all the fre- 
quencies along each horizontal array, we will get the frequency 
distribution with respect to the number of pods and it will be 
exactly the same as that found in the preceding exercise (see 
table on p. 404) ; likewise, if we add up the frequencies in the 
vertical arrays, we will get the frequency distribution with 
respect to length of plants. 

The various steps by means of which the constants for length 
of plant and those for number of pods were obtained were 
given in the preceding exercise and need no repetition. They 
are here secured by the "short method" and are given in the 
correlation table. We are here concerned with the finding of 
the constant which will express the degree of correlation between 
these two characters. 

The only new feature of this correlation table, aside from the 
method in which the observations are distributed, is the column 
marked 2P. Each element of this column represents the total 
deviation (from the assumed mean, or guess) of the individuals 
in each array with respect to both length of plant and number of 
pods. Thus, taking the first horizontal array, the 5-14 class 
as regards number of pods, we wish to find how much the in- 
dividuals in this class deviate from the assumed mean for length 
of plants. It is found as follows : — 

3 individuals each deviated by — 30 = — 90 
9 individuals each deviated by — 20 = — 180 
3 individuals each deviated by — 10 = — 30 — 300 
1 individual deviated by + 20 = 20 + 20 

Algebraic Sum = — 280 

All the individuals in this array deviate from the assumed 
mean for length of plants by the algebraic sum of the total minus 
deviations and the total plus deviations, which is — 280, as 
indicated. But each individual in this array with respect to 



Appendix E 417 

length deviated by — 20 from the assumed mean with respect 
to number of pods, and hence we must multiply — 280 by — 20 
to find the total deviation from both assumed means and this 
gives us + 5600. 

All the elements in the 2P column are secured in exactly the 
same way. The third element is zero, since the deviation from 
the assumed mean for number of pods is zero in this case. The 
fourth element comes out a minus quantity according to the 
following calculation : — 

1 X - 30 = - 30 18 X 10 = 180 

11 X - 20 = - 220 5 X 20 = 100 

42 X - 10 = - 420 2 X 30 = 60 

33 X 1 x40 = 40 

-670 2 X 50 = 100 

480 

- 670 + 480 = - 190 X 10 = - 1900. 

The algebraic signs for each quantity must be carefully ob- 
served throughout the calculations. 

Finally, the algebraic sum of all the elements in the SP column 
is determined.^ This will give us the grand total deviation from 
both assumed means for all the individuals, and hence to find 
the deviation for each individual we must divide by 500. Per- 
forming the operation we get = 66.20. 

ouu 

Now all along we have been working from an assumed mean, 
or guess, and we must apply a correction, which, mathematicians 
tell us, must be the product of the correction for length by that 

1 The elements of the SP column can be obtained by finding the total 
deviation of each vertical array with respect to number of pods and 
multiplying by the deviation of that array with respect to length, instead 
of vice versa. The elements will be different, but their sum will be 
exactly the same by either method. 
2e 



418 



Plant-Breeding 






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ff) 1 . t^ ■^ Oi CO 

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o 

lO 


S^ 


1 1 






II II II II II II II 












CD O 


05 lO O (N lO CO 


o 






1—1 Tjl 


CO i-H rJH rH 


Q 






1— 1 


rH »— 1 


■^005 


1 08Z -| 00^811 


















<M rH r-H (M 


9 


og 


008 OLfZ + 


00051 


00 














■* 








oo 


1— 1 


■^ rH CO (M 


n 


0^ 


0^^ 


009ZI 


t> 














;^ 












t>. (M rH rH 


IT 


08 


088 


0066 


CD 














•># 








CO 


rH CD 


TtH lO CO CO CO 


88 


OS 


091 


00S51 


»o 














:t 








1 


I— t 


CO 00 LO rH oq 


^9 


01 


0^9 


00^9 


•* 














•* 








1 


O 

CO 


iO CO CO CO i-H 

rfl CO rH 


gsT 











CO 






691 


01 - 






•<* 

CO 


CO •* 


O <M O rH 
lO •* rH 




0691 - oes8 - 


00691 


<N 














■<** 










CO 


TtH rH rH 
rH rH 


Zl 


os- 


O^^T - 


0088S 


I— 1 














■* 








i-H 
J. 


CO 


f-H 


f 


08 - 


051 - 


0098 




-* Tt^ 


^ ^ ^ ^ ^ ^ 










> 


1 1 

T-H 


CO '^l lO CD t>- 00 
1 1 1 1 1 1 

lO lO lO »o lO »o 

(M CO ■* iCl CO J^ 


i 


0-A 


(D-A) } 


ziO-A)} 








spoj JC 


jaqiur 


^N 


9'Q2 = D 







Appendix E 419 

for number of pods. This product is always subtracted from the 
quotient of — 

66.20 - (1.88 X - 1.56) = 69.1328. 

Now this corrected deviation must be secured in terms of the 
standard deviations for each character, and hence this quantity 
69.1328 is to be divided by the product of both standard devia- 
tions : — 

69.1328 



14.9789 X 12.0360 



= . 3835. 



We have now finally arrived at our correlation coefficient, 
designated universall}^ by the letter r, the fomiula for the deter- 
mination of which is as follows : — 

-^ - Ci C2 

Correlation Coefficient (r) = 



0"l 0"2 

Like all other constants the correlation coefficient must be 
accompanied by its probable error, the formula for the finding 
of which is as follows : — 

^ ^ ^ .6745 (1 - r^) 

Vti 

Solving this for our correlation coefficient, we ffiid the prob- 
able error to be ± .0257. 

The amount of confidence which can be placed in the corre- 
lation coefficient depends upon the size of its probable error 
largely. Biometricians saj^ that in order to be of much value, 
the coefficient must be from five to ten times as great as its 
probable error. But whether the coefficient shows a high, low, 
or intermediate degree of correlation between the two charac- 
ters measured depends entirely upon its position with reference 
to its two limits, and + 1 or and - 1. According to the 



420 



Plant-Breeding 



size of r found jor the data used in our problem, the correlation 
existing between the length of plant and its number of pods is 
not great. 

Exercise 4 
Statistical Study of Apples from Different Trees 

Object. — To study the individuality of fruit trees. 

Materials. — Apples representing the total product of different 
trees ; scales ; calipers. 

Fill in the following form for each tree. Plot curves repre- 
senting the entire population of trees. 



Name of Variety 



Tree no. 

Age of tree 

Condition of tree ... 

Total number of apples 
Number of marketable apples 
Total weight of apples 
Weight of marketable apples 
Average width of 50 apples 
Average length of 50 apples 

Color 

Any other noticeable differences 



Exercise 5 
Statistical Study of Branches of Different Trees 

Object. — To continue the study as outlined in Exercise 4, 
to test the individuality of trees. 

Materials. — Fruit trees of different kinds, preferably dwarf 
trees; tapes. 

Measure the new growth of various parts of each tree and of 
different trees. Plot curves of each tree and of all of the trees 



Appendix E 



421 




Fig. 108. — A common form of ragweed. 



422 



Plant-Breeding 




Fig. 109. — Another form of ragweed. 



Appendix E 423 

as a population, to show graphically the extent of bud variation 
present. 

Exercise 6 

Statistical Study of the Quantity of Grapes from Different Grape 

Vines 

Use the same general method as in Exercise 4. 

Exercise 7 

Study of Variation in Pressed Specimens of Ragweed or Some 
Plant showing Many Different Types 

Object. — Careful study of the large and small variations among 
different biotypes of ragweed {Ambrosia artemisiifolia) . 

Materials. — Specimens of many different types of the above 
plant or any species of plant which is rich in biotj'pes. These 
specimens should be carefully pressed and mounted. (See Figs. 
108 and 109.) Have each student make detail drawings to show 
minute differences. 

Exercise 8 

Study of Bud Variations and Reversions in Ferns 

Object. — To determine the nature and amount of reversion 
from the parental type, and if possible to find some cause for 
the same. 

Material. — Obtain specimens of the sword fern {Nephrolepis 
exaltata) and Boston fern {Nephrolepis bostoniensis) and as many 
of the other ferns named below as possible. 

Study the trueness to type of each variety' and any reversions 
which they may contain. Draw typical specimens. 

The following is the history, according to Cogswell, of some 
of the fern varieties. This is not a complete list but gives 
an idea of the origin of a few common horticultural varie- 
ties. 



424 



Plant-Breeding 



Nephrolepis bostoniensis .... 

Nephrolepis Piersonii 

Nephrolepis elegantissima 

Nephrolepis Scottii 

Nephrolepis Barrowsii .... 
Nephrolepis Whitmanii .... 
Nephrolepis todeaoides .... 
Nephrolepis superbissima 

Nephrolepis Scholzelii 

Nephrolepis Pruessneri .... 
Nephrolepis magnifiea .... 
Nephrolepis elegantissima eompaeta 



Sport of 



nephrolepis 

exaltata 

(sword fern) 

bostoniensis 

Piersonii 

bostoniensis 

Piersonii 

Barrowsii 

Whitmanii 

Scottii 

Scottii 

Whitmanii 

Whitmanii 

elegantissima 



Exercise 9 
Study of the Morphology of Different Kinds of Flowers 

Object. — To acquaint the student with floral parts and their 
functions. To determine the proper condition of the buds and 
flowers for emasculation, crossing, etc. 

Material. — Buds and flowers of various kinds and in different 
stages of development ; microscope or hand lens ; set of dis- 
secting instruments. The material should represent different 
natural families or orders. 

Have the students make careful drawings of the floral organs, 
of various types of flowers. Take special care to distinguish 
the stamens and pistils. 

The following outline by Dr. M. J. Dorsey may be found 
helpful in this exercise : — 



Appendix E 425 

Study of Flowers (prerequisite to crossing) 

Flower — 
Non-essential organs — 

Calyx — composed of sepals. 
Corolla — composed of petals. 

Essential organs — 

Pistil — f carpels. 

a, style ; b, stigma ; c, ovary { placenta. 

I ovules. 

Stamens — composed of 

£1 , , , , f loculus or cell. 

a, filament ; b. anther < 

I pollen. 

Degree of cross-relationship. — 

1. Self- or close-fertilization. (Occurring in perfect or her- 
maphrodite flowers.) 

2. Cross-fertilization. (Between individuals of same species 
or variety.) 

3. Hybridization. (Between species and sometimes between 
varieties which are very distinct.) 

Causes of sterility. — 

1. Stamens and pistils maturing at different times. (Di- 
chogamy.) 

2. Lack of affinity between pollen and stigma. 

3. Scanty or insufficient pollen. 

4. Lack of viability of pollen. 

Relative position between stigma and anthers. — 
L Stigma and anthers the same height. 

2. Stigma above anthers. 

3. Stigma below anthers. 



426 Plant-Breeding 

Relative maturity of pistil and anthers. — 

1. Both maturing at same time. 

2. Stigma matures first — protogyny. 

3. Anthers mature first — protandry. 

Methods of pollination. — 

1. Insects. 

2. Wind. 

3. Water. 

4. Self-pollination. 

Types of plants in regard to sex. — 

1. jSIonoecious (both sexes on same plant). 

2. Dioecious (each sex on different individuals within the 
species or variety). 

3 . Polygamous (perfect and imperfect flowers on the same plant) . 

Types of flowers in regard to sex. — 

1. Imperfect (1) Staminate — bearing only stamens. 

(2) Pistillate — bearing only pistils. 

2. Perfect or hermaphroditic — bearing both stamens and 
pistils. Determine the following : — • 

{a) Number of parts of flower. — 

a, sepals ; b, petals ; c, stamens ; d, pistils. 
(6) Type of flower — perfect (hermaphrodite) or imperfect, 
(c) Relative position of stigma and anthers. 
{d) Relative maturity of pollen and stigma, 
(e) Is the flower pollinated by insects, wind, or selfed? 
(/) Draw the essential organs and label each part. 

Exercise 10 

Technique of the Cross-pollination of Plants 
This exercise may be carried out in the winter in a green- 
house or conducted in the fall and spring out of doors, where 



Appendix E 427 

additional expense is not involved in growing the plants under 
glass. 

The following suggestive directions may be given to each 
student : — 

Materials. — 1. Instruments: tweezers; scalpel; small, sharp- 
pointed scissors, hand lens, etc. 

2. For covering flowers : ^Manila bags, waxed paper bags, 
cheese cloth, etc. Wire labels, stringed tags, fine copper wire 
or twine cut into short lengths may be used to fasten the bags. 

Preliminary study of -plant. — 

Before attempting to cross plants, it is necessary' to know the 
structure of the flower to be used. To do this {A) locate 
all parts — sepals, petals, anthers, filaments, stigma, style, 
ovar\^; {B) determine whether the flowers are perfect or 
imperfect; (C) learn to recognize the "ripe'' or receptive 
condition of the stigma and pollen. 

Technique. — 

{A) Emasculation. (Unnecessary' where stamens and pistils 
are borne on different flowers.) For crossing purposes 
select flowers in which the anthers have not opened. Re- 
move the anthers with tweezers or scalpel, taking care not 
to injure the stigma. It may be necessary' to remove part 
or all of the petals in some flowers in order to get at the 
anthers, but it is best to remove only the anthers, if possible. 

{B) Bagging. After the anthers have been removed, the 
flower should then be covered with some material, as a 
manila or oil paper bag, to prevent the entrance of foreign 
pollen. When the stigma is receptive, remove the covermg, 
pollinate with the desired pollen of known purity, and im- 
mediately cover again, leaving cover on until fertilization 
has taken place — as indicated by withered or broAisTiish 
stigma. It is desirable to remove the covering when the 
cross has "set." 



428 Plant-Breeding 

(C) The record. The record should include a description of 
each parent, giving particular attention to the contrasted 
characters. Colors may be recorded by comparing with a 
standard color chart. The female parent should always be 
mentioned first. The record on the label should include 
variety name or number of each parent, date of emascula- 
tion, and pollination. (Name of worker can also be placed 
on the label.) As far as possible reciprocal crosses should 
be made. 

Exercise 11 

Embryological Studies from Slides showing Cell Division at Dif- 
ferent Stages, Chromosomes, Pollen Mother-cells, Development 
of the Embryo-sac, etc. 

Provide each student with a high-power microscope and mi- 
croscopic slides mentioned above. Careful drawings of each slide 
should be made. 

Exercise 12 

Study of Pollen Germination and Fecundation 

Materials. — Fresh and preserved flowers showing structure 
of carpels in cross and long section ; microscopic slides showing 
growth and penetration of pollen tubes into ovary, fecundation, 
etc. For study of germinating pollen, fresh pollen may be 
germinated in sugar solutions of various strengths mounted in 
the cells of hanging-drop slides. If this is done at the beginning 
of the practicum, the germinated pollen will be ready for ex- 
amination before the end of the period. 

Careful drawings of all stages observed should be made. The 
drawings should show all the differences in the length and size 
of the pollen tube in various degrees of concentration of the sugar 
solutions. Note also the effect of temperature and other external 
influences upon germination. 



Appendix E 429 

Exercise 13 

Practice in the Cross-pollination of Apples, Pears, Peaches, 

Plums, etc. 
To be carried on in the spring, when the trees are in bloom. 
For general methods of procedure, see Exercise 10. 

Exercise 14 

Purpose. — To teach the Laws of Probability; dominance 
and recessiveness; segregation and recombination; presence 
and absence hypothesis; inhibitory factors; complementary 
factors ; inversed ratios, etc. 

Materials. — Coins, wrinkled and smooth peas, both yellow 
and green m equal numbers for two character pairs ; yellow and 
white kernels of both dent and flint corn ; a pack of playing 
cards; and chemicals. 

Program. — The instructor should take special care to make 
clear the significance of each step in the exercise and their con- 
crete application to problems of plant-breeding and genetics. 

1. The Law of Probability is taught by tossing coins. Each 
student should toss one coin for 2 or 3 minutes and record the 
number of times it faUs head, and th6 number of times tail. 
Then the total for the whole class is summed up. It will be 
found that the latter count, including more tosses, approaches 
the theoretical ratio much more nearly. This should be ex- 
plained by the instructor. 

2. Then in the same way two coins may be tossed by each 
student. He now records heads ; heads and tails ; tails. 

The application of this law in the formation of gametes should 
be made clear by the instructor. 

3. Now the material may be changed by way of illustration. 
Peas or corn comprising two allelomorphs may be used for this 
exercise. They are mixed together in equal numbers in a bag 



430 Plant-Breeding 

and each student draws blindly from the bag one seed at a time, 
recording his draw. This exercise illustrates segregation and 
the formation of gametic cells. 

4. Now each student may remove simultaneously one pea 
from each of two bags, and lay them down side by side to illus- 
trate the mating of gametes in an Fx hybrid and the subsequent 
recombination of characters. He should record only the domi- 
nant characters present in each pair taken and his record will 
show the phenotypes of his F^ hybrids. 

5. The same principles can be illustrated by the use of a pack 
of playing cards. Draw at random two cards at a time. Record 
each combination observed. Two blacks coming simultaneously 
represent a homozygous black individual; a black and a red 
represent a heterozygous form appearing as black, two reds 
represent a pure recessive. For illustrating the combination of 
two character pairs, four cards may be drawn at a time. 

6. Some simple chemical reactions ^ afford an excellent series of 
demonstrations illustrating the main features of Mendelism. 
The following apparatus and chemicals are required : — 

4 500 cc. flasks 3 dozen test tubes 

1 100 cc. flask 4 small funnels for burettes 

1 100 cc. graduate 1 iron stand and clamps 

4 50 ee. burettes 3 test tube racks 

1 2 cc. pipette 1 pipette dropper 

500 cc. 10% ep. NHaOH 500 cc. 5% cp. HCl 

500 cc. 25% cp. NH4OH 100 cc. 2% litmus powder 

500 cc. 10% cp. HCl solution 

10 cc. phenolphthalein 

While the burettes are not absolutely necessary, they will 
greatly facilitate the demonstrations. The solutions are to be 
made up beforehand by the instructor, who should try some pre- 

1 This portion of the exercise is based on an article by G. H. ShuU, 
" A Simple Chemical Device for illustrating Mendelian Inheritance," 
Plant World, 12: 145-153, 1909. 



Appendix E 



431 



n 



nEMO/V5T/lAT/DN O^ ALLeLLDMDffrti/^ 
AND OF COMrLETE UOM/NANCE 



n7=f IT 



/7 



vn n 



O'^rnE^s 



TJ 1 



nn T 




JJFf 



nn 



m 



■ 



Ff 



77 



77/7 



Fig. 110. 



432 



Plant-Breeding 



OEMON5rF?Ar/ON UF FF7E5ENCE AND ABSENCE HrFOrHE5/5 
AND nF /NTEFMEO/ACr 



I 



cf 



r A 



m 



r A 



r a 




a. T 



v^ 



A A 



FT 



A a 



A a 



a a 



^ 



EDMFLEMENTAFr FACTOFS 



TTT A 



\^ 



A 3 



I 
m 
F \ 

Fig. 111. 



G TTT 



Appendix E 433 

liminary experiments to see whether or not the strengths of the 
solutions are correct. They may have to be varied slightly. 
The contents of each test tube representing a gamete (labeled in 
the accompanying figures) are given below. In order to secure 
the simple 3 : 1 or 1 : 3 ratio in F^, eight test tubes representing 
the gametes of Fi are necessary in each case. It is of course 
impossible to represent the phenomenon of segregation in Fx 
by using the test tube labeled Fi. The instructor will have to 
explain that after segregation the gametes are exactly the same 
in nature as those of the original parents of the cross, and that 
the hybrid Fi now forms gametes similar to those of both parents, 
in equal numbers. 

{a) Demonstration of Allelomorphism and of Complete 
Dominance (Fig. 110). 

D contains 10 cc. 10% HCl-\- 2 cc. litmus solution. 

R contains 10 cc. 10% NH4OH + 2 cc. litmus solution. 

The dominance of blue over red can be shown by substituting 
5% HCl for the 10 %. 

(6) Demonstration of the Presence and Absence Hypothesis 
and of Intermediacy (Fig. Ilia). 

A contains 10 cc. 10 % NH4OH + 2 drops Phenolphthalein. 
a contains 10 cc. 5% HCl. 

(c) Demonstration of Complementary Factors (Fig. 111b). 
A contains 10 cc. 10% NH^OH. 
B contains 10 cc. H>0 -\-2 drops phenolphthalein. 

Dominance of a character has usually been taken to be indica- 
tive of the presence of a positive factor determining that char- 
acter. But in some cases the absence of a factor, e.g. cases of 
awnlessness in wheat, or hornlessness in cattle, seems to be 
dominant over its presence. To say that the absence of a thing, 

in other words a purely negative condition, is dominant over its 
2f 



434 Plant-Breeding 

a^MONSrmT/ON DF T^/E Ff9£5ENCe nr an /N/i/S/rOfJ FATTOff 



r A 



AI 



^ 



cf 



A / 



A i 



m 



A i 




W 



fi Zyga/es 
A A // '" 

M 



^ m 



r A i 



A / 




A All ] 



A Ali 



(^ 



AI 



AI 



F. ^ 
Fig. 112. 



A All 



W 



Appendix E 435 

presence seems an absurdity. However, to make the facts 
consistent with the presence and absence hypothesis, two expla- 
nations are offered. One consists in assuming the presence of a 
positive inhibitory factor, which prevents the production of the 
character concerned. The other consists in assuming that one 
''dose" of the factor concerned is insufficient to produce the 
result, hence in its simplex or heterozygous condition, the char- 
acter determined by the factor fails to appear, and it is only 
when the factor is in the duplex or positively homozygous con- 
dition that it does appear. The first of these explanations is 
embodied under demonstration (d). The last is embodied 
under the demonstration entitled ''Explanation of So-called 
' Dominance of Absence.' ". 

(d) Demonstration of the Presence of an Inhibitory Factor 
(Fig. 112). 

A contains 10 cc. 2.5 % NH4OH + 2 drops phenolphthalein. 
Ai equals A + 5 cc. 10 % HCl. 

(e) Explanation of So-called "Dominance of Absence" 
(Fig. 113). 

A contains 10 cc. 10% NHaOH -\-Q drops phenolphthalein. 
a contains 10 cc. 10 % HCl. 

After the zygotes of F2 are obtained, in this last demonstration, 
the instructor should add 10 cc. - 10 % NH^OH to each Aa 
zygote of F2 to show that another "dose " of factor A will now 
produce the result. 

Exercise 15 
A Study of Mendelian Characters in Timothy and Oats 

Purpose. — To afford the student concrete illustrations of 
Mendel's laws ; to find unit characters in plants and to see their 
segregation and recombination. 

Materials. — Mature timothy plants of various strains, com- 



436 



Plant-Breeding 



exrLANAT/DN 0/= 50-CALL^0 VOM/NANC^ D^ A33e/VC€'' 



r -4 




/7 w 



a. 1 



'v'^ 



Cf 



DAme/es 



? 



/T Zygo/es 



A 



■^ 



A A 1 



- ii 



w 



w 




Appendix E 437 

prising as great a variety of unit characters as possible. A small 
bundle of stems for each student containing samples from different 
plants. Photographs and mounted specimens. Varieties of 
oats comprising various unit characters that may be readily 
distinguished in hybrid plants, such as black and white grains, 
side and panicled types of inflorescence; also bearded and 
beardless varieties of wheat or barley. Specimen plants of 
parent types should be available for inspection, also specimens 
of the Fi plants. A large number of F^ plants resulting from each 
cross studied should be available for examination by the class. 

Program. — 1. The instructor should first explain the purpose 
of the afternoon's exercise and outline the order of procedure. 
Unit characters are to be studied and illustrated with timothy 
and oats or barley. Dominance, recessiveness (or presence and 
absence), segregation, and recombination can be illustrated here. 

2. At this occasion a talk may well be given on artificial 
crossing of small cereals for the purpose of creating new varieties. 
The instructor may describe the inflorescence of the oat plant, 
and the technique of making crosses in these plants. He should 
illustrate the talk with charts and with diagrams made on the 
blackboard. 

3. Mounted specimens of oat types together with the Fi and 
F2 progeny resulting from their crossing may be handed around 
for examination by the class. If enough mounts are available, 
the specimens may be drawn and described by each student. 

4. Composite samples of timothy should be handed to each 
student. He should study them to see what diversity of unit 
characters can be found there, in the nature of differentiating 
botanical characters. A list should be made of all the unit 
characters observed. Drawings of timothy heads may help to 
train his observation and fix the idea. 

5. A large progeny of F2 oat plants should be distributed 
among the class after the parent types have been shown and their 
differentiating characters discussed. The class may now examine 



438 Plant-Breeding 

the plants given to them, and sort out the segregated characters. 
When sorting has been completed, the counts for the whole class 
may be ascertained. It should serve to illustrate the expected 
theoretical mendelian ratio. 

Remarks. — Timothy affords very good material for this prac- 
ticum, especially when bundled and mounted specimens, together 
with photographs, are available. 

Oats exhibit excellently contrasted unit characters, but expe- 
rience shows them rather poorly adapted for class study, except 
when mounted specimens are used. The reasons for this are : — 

1. Side and panicled characters — the specimens are often 
pressed out of shape, due to drying and storing, and are, therefore, 
difficult to distinguish, 

2. Color. — Black oats crossed with white give oats of inter- 
mediate color which are often difficult to distinguish from black. 
White and yellow are impossible of being distinguished by the 
inexperienced student. Moreover, color in oat hulls varies 
greatly with the seasonal conditions under which it was grown. 

3. Plants are likely to become broken up in handling, thus 
spoiling the count when mendelian ratios are expected. The 
first two of these objections can be obviated by using mounted 
specimens. Other characters such as naked, hulled, awned, and 
awnless can be illustrated in this way. Probably a better exer- 
cise would be given by substituting corn for oats. 

Exercise 16 

Mendelian Problems 

Purpose. — To enable students to become familiar with what 
might be called the mechanics of mendelism by working out 
mendelian problems by the method of squares. 

Problem. — Given : Two pairs of contrasted characters — 
Tall vine (J"), dwarf vine (t) ; Yellow seeds (Y), green seeds (y) . 
Tallness and yellowness are completely dominant characters. 



Appendix E 



439 



1. What gametes will be formed by an Fi hybrid individual 
from the cross between tall, green and dwarf, yellow ? 

2. How many offspring will it be necessary to grow in order 
to allow every combination to appear in the second generation ? 

3. How many genotypes will there be? 

4. How many phenotypes will appear? 

5. In what ratio will the phenotypes appear ? 

6. How many pure dominant individuals ? 

7. How many pure recessive individuals? 

8. If the combination T X t gave plants of medium height 
when a tall plant with yellow seeds is crossed with a dwarf plant 
with green seeds, how many genotypes will appear in i^2? How 
many phenotypes ? In what ratio ? 

Illustrative 'problems. — The following problems may be studied 
by way of illustration. These are taken from actual cases with 
the tomato, but will apply in principle to other plants, by sub- 
stituting other unit characters : — 

Problem 1 . — 

Tall, homozygous (T) X dwarf, homozygous {t) = Tt; Fi 
Fi gametes = T ; t 
Fi selfed = 

Pollen-grains 



T 



Egg-cells 



TT 


tT 


Tt 


tt 



440 



Plant-Breeding 



1 tt. 



Phenotypes (visible types) (2'») = S TT ; 1 tt. 
Genotypes (actual types) (3") = 1 TT ; 2 Tt 

Problem 2. — 

Heterozygous Tall (Tt) X homozygous dwarf (tt). 

Whenever a plant which is already heterozygous is used as a 
parent, its gametes will become segregated during their formation, 
and when the crossing takes place more than one kind of progeny 
will be produced. In this case the female parent will produce 
two kinds of egg cells, namely, tall and dwarf. 

Graphically, this cross may be represented as follows : — 

Pollen Grains 
t t 



Egg Cells 



Tt 


Tt 


tt 


tt 



The male parent is pure dwarf, therefore all of the pollen grains 
will represent dwarfness only. 

Phenotypes = 2 Tt; 2 tt. 
Genotypes =2 Tt; 2tt. 

If the female parent were crossed with a homozygous tall 
instead of a dwarf, the visible types the first year after crossing 
would all appear the same (tall) instead of two kinds as above. 
There would be 

Phenotypes = 4 f T. 
Genotypes = 2 TT ; 2 Tt. 



Appendix E 



441 



Problem 3. — 

The cases which have been considered hitherto show perfect 
dominance of one unit over another. This is not always the 
case. It frequently happens that the first generation hybrid 
is intermediate between the two parents, and in the second gen- 
eration the heterozygote forms differ from either homozygous 
form. Thus when large, round tomatoes are crossed with small, 
plum-shaped ones, the Fi hybrid is intermediate between the 
parents. If L represents largeness and (Z) small, plum-shaped, 
then Fi hybrids (LI) will not be the same as (LL), but will be 
distinctly different. The formulae previously given, 2", 3", etc., 
will not hold in cases of incomplete dominance. This will be 
more fully explained later. Large (L) x small, plum-shaped 
(l) = LI, an intermediate type of fruit. 

Fi gametes = L, I. 
Fi self ed = 

Pollen Grains 

L I 



Egg Cells 



LL 


LI 


LI 


11 



Phenotypes = 1 LL; 2 LI; 1 II 
Genotypes = 1 LL; 2 LI; 1 II. 

Problem 4. — 
Intermediate {LI) X Large, round {LL) 



442 



Plant- Breeding 



Pollen Grains 
L L 



Egg Cells 



LL 


LL 


LI 


LI 



Phenotypes =2 LL] 2 LI 
Genotypes = 2 LL ; 2 LI. 

Problem 5. — 

Tall, smooth (Th) X dwarf, Hairy (tH) = Tall, Hairy (TtHh) 

Fi gametes = TH; Th; tH; th. 

Fx self ed = 

Pollen Grains 

TH Th tH th 



TH 



'% Th 

H 

o 

ItH 



th 



TT 
HH 


TT 
Hh 


Tt 
HH 


Tt 
Hh 


TT 
Hh 


TT 

hh 


Tt 
.Hh. 


Tt 
hh 


Tt 
HH 


Tt 
Hh 


tt 
HH 


tt 
Hh 


Tt 
Hh 


Tt 
hh 


tt 
Hh 


tt 
hh 



' Appendix E 



443 



Phenotypes (2«) = 9 TH ; 3 Th; S tH ; 1 th. 
Genotypes (3«) = 1 TTHH, 1 TThh, 1 UHH, 1 tthh, 2 TTHh 
2 UHh, 2 7^^/i/i, 2 r^Fiy, and 4 7^^^/^. 

Problem 6. — 

Tall (Heter) i smooth (T^^/i) x dwarf, Hairy (tH). 
Female gametes = Th, th. 
Male gametes = tH. 



Pollen Grains 
tH 



Egg Cells 



Th 



th 




It will be seen that two types are produced the first year after 
crossing instead of the one where pure parents are used. Segre- 
gation takes place immediately in the female parent because of 
its hybridity, and two kinds of gametes will be produced. 

In order to get a comparison with the F. when pure parents 
are crossed, it is necessary to self both types as follows : — 

(a) TtHh produces gametes as follows, Th, Th, tH, th. These 
are the same as in problem 5 and hence the resulting plants will 
be: — 

Phenotypes =9TH,S Th, 3 tH, 1 th. 

Genotypes = 1 TTHH, 1 TThh, 1 ttHH, 1 tthh, 2 TTHh, 
2 ttHh, 2 Tthh, 2 TtHH, and 4 TtHh. 

(b) ttHh produces the following gametes: tH, th. 

^ "Heter " is used for short in place of heterozygote, similarly "homo " 
is used for homozygote. 



444 



Plant-Breeding 



Pollen Grains 
tH th 



IH 



Egg Cells 



th 



It 


tt 
Hh 


tt 
Hh 


tt 
hh 



Phenotypes = ttHH, ithh. 
Genotypes = tlHH, 2 UHh, 1 tthh. 

Problem 7. — 

Tall, large-round (TL) X dwarf, small plum-shaped (tl) = Tall 
intermediate (TtLl). 

Fi gametes = TL; Tl; IL; tl 



Pollen Grains 
TL Tl tL 



tl 



Egg Cells 



TL 



Tl 



tL 



tl 



TTLL 


TTLl 


TILL 


TtLl 


TTLl 


TTll 


TtLl 


Ttll 


TILL 


TtLl 


ItLL 


ttLl 


TtLl 


Ttll 


ttLl 


till 



It must be remembered in this problem that we have incom- I 
plete dominance in one allelomorphic pair, therefore the number 
of visible types is different than in cases where both units exhibit 
dominance. 



Appendix E 



445 



Phenotypes = 3 TTLL, 6 TTLl, 3 TTll, 1 ttLL, 2 ttLl, 1 ttll. 

Genotypes = 1 TTLL, 1 TTll, 1 ^^LL, 1 ttll, 2 TTL/, 2 Ttll, 
2 r^^/, 2 «L/, and 4 T^L/. 

What visible types would be produced if incomplete dominance 
occurred in both characters? 

Problem 8. — 

Self-fertilize-Tall, intermediate (TTLl). This is a pure tall, 
hence all of its progeny will be tall. 

Pollen Grains 
TL Tl 



Egg Cells 



TL 



Tl 



TTLL 


TTLl 


TTLl 


TTll 



Phenotypes = 1 TTLL, 2 TTLl, 1 TTll. 
Genotypes = 1 TTll, 2 TTLl, 1 TTll. 

EXEECISE 17 

Ear-to-Row Test with Corn 
Field Practicum 

Purpose. — To demonstrate to the student the method of 
testing out the transmitting power of individual plants; to 
show him how a breeding plot should be arranged for corn ; to 
teach him how to harvest the corn and make notes on which 
to base his selections. A practical demonstration of the method 
of pure line selection. 

Materials. — For each student a sack for holding ears, wired 
tags and strings for tying sacks, and sheets for taking data. A 
wooden rack with spikes for drying ears of corn. Grocery scales 
for weighing the ears from each row. 



446 



Plant-Breeding 



Data Sheet for Corn Selection 
(Ear-to-Row Method) 
Mark Dent (+) ; mark Flint (F). 



No. of row 
Total no. of hills 
Total no. of stalks 
No. barren stalks 
Total no. of ears 
Total wt. of ears 
No. mature ears 
Wt. mature ears 
No. immature ears 
Wt. immature ears 
Percentage mature ears 
Percentage immature ears 




Choose 10 of the best-looking ears from one row on which to 
take the following data : — 



Wt. of ears 
Length of ears 
Circumference ^ of ears 
No. of rows per ear 
Wt. of shelled corn 
Wt. of cob 



A field plot planted by the ear-to-row method, saving unused 
half of each ear for comparison with its progeny. It should 
contain two or more rows, as space permits, for each student. 
Each row should contain 50 hills. The rows should be planted 



^ Circumference should be measured at a point about ^ of the distance 
from the butt toward the tip. 



Appendix E 447 

and cultivated under regular field conditions. Two buffer rows 
should be planted completely around the plot. These should 
be cut and discarded before the interior rows of the plot are 
studied. Their purpose and use should be explained to the 
class. 

Program. — After the instructor has explained the purpose of 
the practicum, and the manner of procedure for the afternoon, 
the class may be taken to the field. Each student should have 
one or two rows for himself. Students may be permitted to 
work in pairs, if desirable. Careful and detailed notes should 
be made on each row and recorded on data sheets provided for 
that purpose. The corn may be taken back to the laboratory 
for weighing. Statistics for the whole plot should then be 
compiled, so that the individuality of different rows can be 
compared. The student should select 10 of the best ears from 
each of his rows and put them on the drying rack provided. 
These ears are to be used later for a study in the laboratory. 

EXEKCISE 18 

Corn-judging 

Students of plant-breeding should be trained to have a critical 
judgment of agricultural and horticultural plants. Exercises 
in comparative judging are the best way to attain this end. 
Utility should be kept constantly in mind. 

Details of corn judging will not be given here ; they are too 
well known to need emphasis. For the East, both dent and 
flint varieties should be used. The ears which are judged in 
this exercise may be the ones the student himself has previously 
harvested from the ear-to-row plot. The best ten ears should 
be used for Exercise 19, which should always accompany exer- 
cise 18. 

Object. — To encourage critical judgment of corn and, by the 
same means, of other crops. 



448 Plant-Breeding 

Materials. — Ten ears of different races and types of corn to 
each student ; tape, scales, charts, etc. 

Each student should score a sample of flint corn according to 
the following score card : — 

New England Flint 

Points 

Maturity and seed condition 20 

Uniformity (or regularity of single ears) 15 

Kernels 15 

Weight of ear 10 

Length and proportion 10 

Tips 5 

Butts 10 

Sulci (space between rows) 10 

Color _5 

Total 100 



Exercise 19 

Statistical Study of Ears of Corn 

This should accompany or follow Exercise 18. 

Object. — (a) To study critically and statistically the various 
parts of ears of corn, (b) To work up these data by biometrical 
methods, drawing curves, and ascertaining mean, standard 
deviation, coefficient of variability, etc., for the various parts 
of the ear. (c) To illustrate testing for germination. 

Materials. — Each student should be given the same ears of 
corn which he had for Exercise 18 ; tapes, scales, etc. 

The following form should be filled in by each student : — 

Note. — This should not be merely a mechanical process, but 
the student should give each step very careful thought. These 
tables are given to assist in organizing the student's method and 
his thinking, but not to replace them. Do not study the method 
but the plants. Consider carefully the significance of each step. 



■' A 



Appendix E 



449 



Study of Corn 
Variety: Dent, flint, sweet, pop. (Underline.) 



Where grown 

(a) Length of ear in cm. 

(b) Circumference of ear in cm. (^^ butt to 

tip) 

(c) Weight of ear 

(d) Number of rows 

(e) Circumference of cob (l buti to tip) 
(/) Weight of shelled corn 

(g) Weight of cob 
(h) Percentage of shelled corn 
(?■) Total number of kernels 
(j) Average weight of kernel 
(/c) Width of kernels in cm. (taken at ran- 
dom) 
(/) Compute average width 
(m) Length of 50 kernels in cm. (taken at 

random) 
(n) Compute average length 



Exercise 20 
Study of Correlations of Characters in Corn 

Use the same data as employed in Exercises 17 and 19. Make 
correlation tables by accepted biometrical methods of such 
characters as length and circumference ; length and number of 
grains ; weight and number of grains ; length and weight ; etc. 
Work out correlation coefficients. 

Object. — To find out if certain characters are associated so 
that a measurement of one will give an indication of the other. 

Materials. — Data from Exercises 17 and 19 ; cross-section 
paper. 

2g 



450 Plant-Breeding 

Exercise 21 

Corn Selection — Laboratory Study 

Purpose. — To give the student an understanding of the 
qualities that constitute a good ear of corn ; to teach the bene- 
fits and dangers of cross-pollination. 

Material. — For each student : 1 tape measure ; 1 scalpel ; 
1 hand lens; 10 ears of corn selected from a row in breeding 
plot; samples of various types and colors of corn. These 
should have been shelled and soaked in water for 24 hours pre- 
vious to this laboratory period in order to render them easy to 
dissect. Cobs of corn bearing mixed kernels to illustrate zenia ; 
scales ; data sheets ; germinator. 

Program. — The instructor should first explain the purpose 
of the practicum and outline the afternoon's work. He should 
explain the structure of a kernel of corn, calling attention to 
the difference between the various types of corn and the ad- 
vantage of certain shaped kernels. Fecundation should be 
thoroughly discussed, and its effect in causing zenia. Illustrate 
with diagrams, charts, and specimens. 

Discuss the dangers of mixing varieties by close planting. 
The danger of close fertilization and the stimulus resulting from 
cross-fertilization should also be discussed. 

The advantage and manner of making germination tests 
should be explained. 

The student should remove 6 kernels from each ear and place 
them in the germinator to be examined later, at which time he 
should record the percentage of germination. 

Questions and problems concerning zenia printed on the 
outline sheet should be answered in a written report. 

Laboratory Directions for Corn Study 

1. Complete taking data on 10 ears of corn. Compare with 
remnant half of parent ear. From your data select the best 
3 ears for breeding purposes. 



Appendix E 451 

2. Remove 6 kernels from each ear for germination test, 
along a spiral line from 1 inch of butt to near the top, revolving 
the ear twice. 

3. Draw a typical kernel. 
{a) Face aspect. 

(6) Side aspect. 

4. Make and draw longisections through the middle line 
both ways of the kernel, showing the following structures : — 

(a) Mass of starch or endosperm. 

(6) Crescent-shaped body, the germ or scutellum near the 

smaller end of the grain, 
(c) Remaining portion of embryo lying in the depression 

between scutellum and seed-coat. 
{d) In sample kernels where does color lie, in the pericarp, 

aleurone layer, or endosperm ? 
(e) Note relative amount and position of starchy and 

horny endosperm in 

1. flint kernel, 

2. dent kernel, 

3. pop-corn kernel, 

4. sweet-corn kernel. 

5. How would an i^i kernel of corn appear in a cross between 



white sugar X yellow flint ? 

yellow flint X white sugar ? 

white flint X purple flint ? 

purple flint X white flint ? 

red sweet X purple flint ? 

purple sweet X red flint ? 

Dominant Characters. — 

Colored over white. 
Yellow over non-yellow. 



452 Plant-Breeding 

Red pericarps may conceal purple aleurone. 
Purple in aleurone over red in aleurone. 
Starchy over non-starchy. 



Exercise 22 

A Study in Potato Selection 

Purpose. — 1. To teach the essential characteristics of a good 
tuber and a good tuber-line. 

2. To teach the principles of selection by a study of variability 
in pure tuber-lines. 

3. To demonstrate the tuber-unit method of potato selection. 

4. To study variability by means of biometrical data, and 
the interpretation of constants and curves derived therefrom. 

5. To fix in mind how the hills of different weights look. 

6. To calculate the theoretical weights per acre when given 
certain weights per hill. 

First Exercise 

Materials. — Printed directions and sheets for recording data. 
Manila paper bags, size 12, for containing product of each hill. 
Cloth bags for carrying a number of these small bags when filled. 

A breeding plot planted by the 4-hill tuber-unit method, 
that is, each four hills having the same progeny-number should 
come from the same mother tuber, and they should be planted 
and staked so that the progeny of each hill and unit can be 
distinguished. 

This plot should be planted in good soil and given excellent 
care throughout the season as its usefulness to the class will 
depend entirely on the condition of the crop at harvest time. 
The rows and tuber-units should be labeled carefully and accu- 
rately in a convenient way, so that they may be made an object 
lesson in record-keeping. 



Appendix E 



453 



a 
o 

<J 

O 
pin 

« 
O 

H 

a 

Eh 






































































- 






















""'] 










6 


•<* 












































' 


CO 














































09 






j 
























1 

1 






















































= 


-= 








1 
i 














































6 


^ 


































1 










eo 


















































M 






























j 




1 










1-1 










i 


























1 


_ 




Unit 
No. 


















































.2 

c 


o 
S3 

s 

O 

o 



ce 

c 

c 
a 


3 
O 
ii 

o 
'> 

c 


>> 

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c3 
(0 
Xi 

03 


a: 

a 

w 

g 


a 
6 


a 


15 
a 

u 

Ci 

3 

<V 

Si 

£ 

"o 

6 
'Z. 


aj 

a 

a: 

03 

s 


2 


a 


IS 
_c 

t- 

o 

'c 
3 

a 

o3 

x: 


IS 
c 

_^ 
5c 

a 


^5 
'*^ 
-5 

G 

o 

o 


S 


"5 

en 


c 
.S 

O 


o 
o 

1 
re 


Ih 

3 
X 

u 

T 

13 


is 
c 

1 


s 

1 


5 

3 

'a 

ca 

d ' 
o 

u 

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o 
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X! 

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>, 
W 


r. 
?; 

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454 Plant-Breeding 

Enough hills should be provided so that each student may 
have for himself several tuber-units. Five to ten units to each 
student will be enough if the student is required to observe and 
compare a large number as they lie in the field. The complete 
data for the whole field should be compiled by the class as a 
whole, and distributed to each student for a comparative study. 

Program. — Just prior to the exercise, each hill should be 
dug carefully and the tubers replaced where they grew, but 
exposed to sight, especial care being taken that no labels be mis- 
placed nor lost. The class may then be taken to the field. 
The instructor should explain the purpose of the exercise, the 
principles of pure-line selection as illustrated here, and the 
method of planting a potato-breeding plot by the tuber-unit 
method. He should give careful instructions for the after- 
noon's work. The class may then examine and compare the 
units as they lie exposed in the rows. The instructor should 
point out such differences as occur. A certain number of tuber- 
units should then be assigned to each student, and he should 
be required to take data from these units, as directed on the 
printed sheets provided. Such data-taking as involves the use 
of apparatus will necessarily have to be postponed until the 
following period, when it can be done in the laboratory. 

Each student should carefully preserve his tubers properly 
labeled for the next laboratory exercise. 

Second Exercise 

Materials. — Data taken in Exercise 1 ; the tubers collected 
in Exercise 1; scales; paper plates (6 for each student). 

Program. — The instructor should first outline the afternoon's 
work. He should explain the qualities that constitute a good 
tuber ; also how that ideal form, size, and color differ in various 
varieties. He should explain a score-card. 

The students may now proceed to finish taking the data on 
the tubers that they collected at the previous laboratory period. 



Appendix E 455 

When the data are complete, they can all be summed up for 
each tuber-unit and the units compared. 

Each student should next make out a score-card embodying 
the points of his ideal unit, and score his units by it. The 
instructor may now give out a score-card by which the whole 
class may score their units alike. 

Make up hills weighing i 1, H, 2, 3, and 4 pounds, and 
draw them natural size. 

Compute the yield per acre from the above weights per hill, 
assuming the hills to be planted in rows 3 feet apart and 18 
inches apart in the rows. One bushel weighs 60 pounds. 

Directions for Report on Potato Selection 

1. Distribute the data for the number of tubers per hill into 

classes. 

2. Determine the mode, modal coefficient, mean, standard 
deviation, coefficient of variability, and their probable errors for 
the number of tubers per hill. 

3. Determine the mode, mean, standard deviation, and co- 
efficient of variability for the number of marketable tubers per 
hill, weight of tubers per hill, and weight of marketable tubers 

per hill. 

4. Draw Quetelet curve, showing frequency distributions for 
number of tubers per hill, number of marketable tubers per 
hill, weight of tubers per hill, and weight of marketable tubers 

per hill. 

5. Distribute into classes the data for the number of tubers 
per four-hill-unit, number of marketable tubers per four-hill- 
unit, weight of tubers per four-hill-unit, and weight of market- 
able tubers per four-hill-unit. 

6. Draw Quetelet curves, showing frequency distributions for 
number of tubers per four-hill-unit, number of marketable tubers 
per four-hill-unit, weight of tubers per four-hill-unit, and weight 
of marketable tubers per four-hill-unit. 



456 Plant-Breeding 

7. Make a transmission curve from the data on the accom- 
panying sheet. Which progeny units would you select for breed- 
ing purposes? How do you account for the apparent discrep- 
ancies which occur, such as the cases where the offspring give a 
very different yield from their parents ? 

8. Taking into account the number of tubers per hill, weight 
of tubers per hill, number of marketable tubers per hill, and 
weight of marketable tubers per hill, select the best 25 four- 
hill-units. Tabulate these, giving their progeny number and 
data for number of tubers per four-hill-unit, number of market- 
able tubers per four-hill-unit, weight of tubers per four-hill-unit, 
and weight of marketable tubers per four-hill-unit. 

9. Give briefly your reasons for selecting the above four-hill- 
units. Draw Galton curves for these 25 four-hill-units, showing 
variation in the number of marketable tubers per four-hill-unit 
and weight of marketable tubers per four-hill-unit. 

10. Determine the possible yield of marketable tubers from 
an acre of the highest and lowest yielding of the 150 four-hill- 
units, also for the highest and lowest and for the average of the 
25 selected units. 

11. Give a short summary of results as shown by the con- 
stants and curves and their bearing on your final selection. 

12. Give direction for starting a potato breeding-plot.^ 

Potato Data for making a Transmission Curve 

The following data have been obtained by the method out- 
lined above. They represent the weights in grams of parent 
hills and the average weight of their corresponding progeny. 
The parent hills have been listed in the order of their weight 
from lowest to highest (forming a Galton curve). 

1 Reference : H. J. Webber, "Plant Breeding for Farmers." New 
York Agr. Exp. Sta., Cornell University, Ithaca, N. Y., Bull. 251 : 
162-171, 1908. 



Appendix E 



457 



Nos. 


Parents 


Progeny 


Nos. 


Parents 


Progeny 


1 


1077 


1463 


26 


1588 


1454 


2 


1106 


1080 


27 


1588 


1615 


3 


1106 


1240 


28 


1616 


1175 


4 


1361 


1881 


29 


1616 


1575 


5 


1361 


837 


30 


1644 


1775 


6 


1361 


1136 


31 


1644 


1807 


7 


1361 


1536 


32 


1644 


1917 


8 


1361 


1605 


33 


1758 


2250 


9 


1361 


1660 


34 


1814 


1660 


10 


1361 


1800 


35 


1871 


1275 


11 


1361 


1895 


36 


1871 


1.80 


12 


1389 


1972 


37 


1871 


1665 


13 


1418 


1696 


38 


1871 


1688 


14 


1418 


1904 


39 


1871 


1750 


15 


1471 


1440 


' 40 


1874 


1555 


16 


1474 


1086 


41 


1874 


1861 


17 


1474 


1215 


42 


1874 


1889 


18 


1474 


1480 


43 


1928 


1440 


19 


1531 


711 


44 


1928 


1481 


20 


1531 


1294 


45 


1928 


1620 


21 


1531 


1574 


46 


1928 


1982 


22 


1531 


1725 


47 


1984 


1575 


23 


1531 


1755 


48 


2041 


1236 


24 


1588 


1320 


49 


2041 


1880 


25 


1588 


1365 


50 


2098 


2365 



Exercise 23 



Study of Citrus Hybrids 

Object. — (a) To study the possibility of obtaining valuable 
kinds of citrus fruits by means of hybridization. (6) To study 
the structure of citrus hybrids as compared with their parents. 
(c) To study the economic value of these hybrids. 

Materials. — Obtain from some of the extreme southern ex- 



458 Plant-Breeding 

periment stations, or from nurserymen or growers, samples of 
citrus hybrids, such as citranges, tangelos, and the like, and 
samples of Citrus trifoliata. Purchase oranges, lemons, grape- 
fruits, and tangerines from the fruit stores. Provide also for 
each student, or group of students, a glass, spoon, sugar, and 
water. 

Compare the hybrids with their parents, with special reference 
to the following points : — 

(a) Fruit — size, shape, color, amount of juice, quality of 
juice, condition of segments, etc. 

(b) Trees (if branches or photos are available) — size, shape, 
branching, kind of leaves, etc. 

(c) General — length of season, resistance to cold, etc. 
Squeeze out the juice from several fruits, add sugar and water, 

and test the adaptability for beverage and other economic 
purposes. 

Exercise 24 

Study of the Results of the Plant-to-Roio Tests of Wheat, Oats, 
Cabbage, Onions, or any Crop where Data are Available 

Exercise 25 

Studies of Origin of Varieties — Corn, Wheat, Apples, Plums, 

Grapes, Etc. 

Literature study of the history of varieties. Methods em- 
ployed to originate varieties should be carefully noted. 

Exercise 26 

Field Trip to Experimental Grounds 

Most experiment stations have plant-breeding experiments 
under way, and if a fall inspection of the plats would be in- 
structive to students, they should be taken on such a trip early 



Appendix E 



459 



in the fall and required to make careful notes, to be written up 
later in the form of a report. 

Exercise 27 

Working Plans for Practical Breeding Experiments 

Object. — To familiarize the student with field methods of 
breeding plants. 

Outline for Timothy Breeding 

First Year. — Select 10 heads of timothy and grow 50 plants 
from each. 

100 ft. 

10 rows. 



40 ft. 



500 plants in 10 rows 100 ft. 
long. Plants 2 ft. apart in 
the rows. 



Second Year. — Cultivate. 

Third Year. — Choose several of the best plants from the best 
two rows, and the one best plant from each of the other rows — 
14 or 15 in all. With the seed from these, plant a ''test plat," 
and plow up the original seedling plat. 

60 ft. 



60 ft. 



15 rows. 
Rows 4 ft. apart — plants 2 ft. 
apart in the rows. 



Fourth Year. — Cultivate the test plat. 

Fifth Year. — Choose 2 or 3 or more of the best rows and save 
separately the seed from each. Plow up the remainder of the 
rows and plant to vegetables. 



460 



Plant-Breeding 



60 ft. 



60 ft. 



4 selected rows. 
Plant I acre multiplication 
plat from each select row. 
Seed them broadcast at the 
rate of 16 pounds per acre. 
Remainder of the plat utilized 
for vegetables. 



Sixth Year. — Use seed from multiplication plats to plant a 
fairly large-sized field. Continue selection of seedlings, if de- 
sired, from select rows according to above scheme. 

Outline for Selective Breeding of Timothy 

First Year. 1 . Manner of procuring seed from starting a selec- 
tion. — When timothy is ripening, go over a field and choose a 
number of good ripe seed-heads from tall, robust culms which 
appear to come from good plants. Also look for exceptionally 
good plants from along the roadsides and fences, and whenever 
they are found, preserve good heads for seed. Choose good seed- 
heads from at least 10 or 12 of these good plants. Thresh the 
seed from these heads, keeping the seeds from each plant sepa- 
rate, and sow them immediately. No time should be lost. 

2. Planting the seed. — The seed should be planted early in 
August. Take small boxes about 2 feet long by 1^ feet wide 
and 4 inches deep ; fill them with good soil from some locality 
where there has been no timothy and thus where there is little 
likelihood of timothy seed being in the soil. Pack the soil down 
slightly in the box and smooth off the top, removing all lumps. 
Plant the seed in the boxes in short rows, placing the rows about 
2 to 2| inches apart. In planting the seed open shallow furrows 
in the soil and sow the seed by hand, arranging so that the seed 
will be only very lightly covered. Sow the seed as thinly as 
possible in the rows and thin out later so that the plants will 



Appendix E 461 

stand about 1 inch apart. Sow enough seed in rows of sufficient 
length, so that when properly thinned there will remain about 
300 plants. If thinned to 1 inch apart, this will require rows 
aggregating 25 feet long. Be careful to keep the seeds from 
each head or plant separate from one another and plainly labeled. 

After the seed is sown, water the seed boxes carefully, using a 
fine spray, in order to prevent washing the seed out. A good 
method is to cover the soil with an open mesh cloth, such as 
cheese cloth, and sprinkle the water on this until the soil is 
thoroughly wet. Then place the seed box in the shade in a moist 
place, such as the north side of the house. It is a good practice 
to keep the boxes covered with paper or glass, until the young 
plants begin to appear. It is important to keep them moist at 
all times. When the young plants are well up, thin them to 
about one inch apart in the rows, leaving the strongest plants. 

The plants should be kept in boxes until about the 20th of 
September, when they should be planted in the field. About a 
week before transplanting they should be gradually exposed to 
the full sunlight in order to harden them up. At this time each 
plant should have 2 or 3 leaves, 3 or 4 inches long. 

3. Transplanting into the field. — Choose a place in the field 
where the plants may remain for at least two years without 
being disturbed. Set the plants two feet apart in rows that 
are four feet apart. By this method the greater part of the 
cultivation can be done with a horse cultivator. In transplant- 
ing the seedlings from the boxes, a time must be chosen shortly 
after a rain, when the soil is well moistened. The plants should 
be set out about the 20th of September, if possible, so that they 
may become well rooted before winter comes on. It may be 
necessary to hoe them before winter, but this is not likely if the 
land is well prepared before planting. 

If 10 heads were originally chosen and 50 plants are grown 
from each head, there should be 10 rows 100 feet long, which 
would occupy a piece of land 40 X 100 feet. 



462 Plant-Breeding 

4. Second Year. Cultivating the seedlings. — In the spring 
the seedlings must be cleaned out very eariy before they are 
hidden by other grasses. The cultivation and hoeing must be 
done at sufficient intervals to keep the ground free from weeds 
and in good condition. These plants will produce a few culms 
each the first summer, which should be cut as soon as they have 
bloomed, in order that the strength shall go into the general 
growth. Do not attempt to select the best plants the first 
season. A safe judgment cannot be rendered until the second 
season. 

5. Third Year. Selecting the best plants. — When the plants 
reach the stage for cutting in the second summer, that is, when 
they are in full bloom, the final selection of the best individuals 
can be made. Examine each row critically in order to determine 
which head or heads have given the best progeny as a whole. 
If any one or two rows are markedly superior to the others, 
choose several of the best plants in each of these rows. Also, 
choose the one best plant in each of the other rows. 

6. Testing the selected plarits as clonal varieties. — In order to 
make a further test of the 14 or 15 best plants, choose another 
uniform plat of fairly good soil between the 5th and 20th of Septem- 
ber and prepare for planting an area of slightly over 60 feet square. 
This plat should be located at some distance from any other 
timothy, preferably 200 to 300 feet. Dig up each selected 
plant ; divide it into slips or clons and plant this new plat with 
them as before, in rows 4 feet apart. Plant one row with slips 
from each selected plant, placing the plants 2 feet apart in the 
rows. Transplant about 30 slips from each of the selected 
plants, so there will be a single row from each about 60 feet long. 
This plat may be designated as "the clonal test plat." 

As soon as this clonal test plat is planted from the selected 
plants, the seedling test plat may be plowed up and used for 
other purposes. 

7. Fourth Year. Cultivation of "clonal test plat.'' — The 



Appendix E 463 

clonal test plat should be cultivated and hoed sufficiently to 
keep the weeds down and to allow the full development of the 

plants. 

8. Fifth Year. Selecting the best clonal rows. — When the 
plants are well headed and are about to begin blooming, the 
final examination can be made. Go over each row carefully, 
and examine it with reference to yield and desirability of type, 
and select the superior row or rows. It will be best to retain 
at least 2 or 3 of the best rows ; or more, if there is but little 
difference in them. Good early-maturing and late-maturing 
rows should be retained if both are present in the test plat. 
When this selection has been made, cut the crop on the dis- 
carded rows immediately so that the pollen from these dis- 
carded rows will not contaminate, by cross-fertilization, the seed 
which is being developed in the selected rows. At any con- 
venient time these discarded rows may be dug up and the space 
filled with new plants grown from cuttings of the chosen plants. 
By a little care and cultivation these select rows can be retained 
5 or 6 years as a source of supply of seed of a superior kind. As 
the rows of selected types begin to run out, or become impure 
by ordinary timothy plants around them, or by other grasses 
growing in the clumps, other or more extended clonal rows 
could be planted from them. 

9. The multiplication plat. — The seed from the select rows 
of the clonal test plat should be sown in the early fall, sometimes 
before the 15th of September in broadcast plats, as large as the 
amount of seed obtained will permit. Sow these plats, at the 
rate of about 16 pounds to the acre. There should be enough 
seed from each row to plant about | acre. 

Sixth Year. — The seed from these broadcast multiplication 
plats can be utilized the next year to plant a fairly large field 
which, if desired, may be harvested for seed to plant still larger 
areas.' These plats may be utilized for seed for several years 
before they run out. 



464 Plant- Breeding 

10. Continuation of the selection. — If the farmer has in mind 
the continuous selection of his seed, with the view of selling his 
seed as improved seed, he should plant small samples of seed 
from each of the selected rows in the clonal test plat. Their 
treatment and subsequent selection should be a repetition of the 
original scheme outlined above. ^ 

General Directions and Questions for Report on Corn 

Breeding 

Suppose you buy a farm of 200 acres on which are growing 
the following crops : potatoes, corn, timothy, and one of the 
three cereals, wheat, oats, or barley. There are 50 acres of 
pasture and woodland. You wish to continue growing these 
same crops, and at the same time to improve them by a scheme 
of selective breeding. Plan the arrangement of fields and breed- 
ing plots for the first 6 years, using the following directions. 
Timothy breeding plots should be 200 to 300 feet from any 
other timothy. Corn plots 1200 feet from any other corn. 
(Why?) Each year should be planned separately, using 
maps and diagrams, but should be included in a definite 
six-year scheme. Observe proper rotations for crops where 
desirable. 

1 . In selecting plants for breeding purposes, why do we choose 
individual plants? 

2. In breeding work, why do we test out the selected individ- 
uals by breeding each one separately? 

3. Why is it most satisfactory for the breeder to work with 
plants that are self-fertilized? 

4. Why do we plant border rows around breeding plots? 

5. Why do we detassel alternate halves of adjacent rows in 
corn breeding plots? 

1 For more detailed directions for timothy breeding, see Webber, H. J., 
" Production of New and Improved Varieties of Timothy." Cornell 
University Agr. Exp. Sta. Bull. 313, 1912. 



Appendix E 465 

6. Why should corn breeding plots be isolated? What is a 
safe distance? 

7. Why should timothy breeding plots be isolated ? What is a 
safe distance? 

8. Is it necessary to isolate breeding plots of the small cereals? 

9. In selection work, what three rules should the breeder 
follow who understands the principles of pure-line breeding ? 

Scheme for Potato Breeding Plots ^ 
First Year. — Choose 500 good tubers. Plant them in a 
breeding plot by the tuber-unit method. Rows should be 3 
feet apart, hills l\ feet apart in the rows. At harvest time 
choose the best 50 units. Save the best 10 from each of these 
units for planting a breeding plot the next year. 

Second Year. — Plant the selected tubers in a breeding plot 
as in the first year. At harvest time discard all poor units. 
Select the best 50 units. Save 10 of the best tubers from each 
of these units for planting the third year's breeding plot. Use 
the rest for planting a field crop the next year. 

Third Year. — Use these 500 tubers to plant a breeding plot. 
Plant your field crop with the remaining choice tubers. How 

1 For details of the following schemes read Cornell University Exp. 
Sta. Bull. 251, "Plant Breeding for Farmers," 1908 ; also Bull. 313, "The 
Production and Improvement of New Varieties of Timothy." 

For cotton breeding, see Webber, H. J., "Improvement of Cotton by 
Seed Selection," U. S. Department of Agr. Yearbook, 1902, pp. 365- 
386. 

16.5 ft. = 1 rod ; 160.0 sq. rd. = 1 acre. 

Plant: Corn, 8-12 qt. per acre; Oats, 2-3 bu. per acre; Wheat, 
2-3 bu. per acre ; Barley, 2-3 bu. per acre ; Potatoes, 12-15 bu. per acre; 
Timothy, 6-8 qt. or 16 lb. per acre. 

Standard weights: Corn, 1 bu. = 70 lb. shelled, or 56 lb. on cob; 
Oats, 1 bu. = 32 lb. ; Wheat, 1 bu. = 60 lb. ; Barley, 1 bu. = 48 lb. ; 
Potatoes, 1 bu. = 60 lb. ; Timothy, 1 bu. = 45 lb. 

Average yield per acre in United States for 1002: Corn, 20.2 bu. ; Wheat, 
15.9 bu. ; Oats, 37.4 bu. ; Barley, 50.4 bu. ; Potatoes, 113.4 bu. 
2h 



466 Plant-Breedings 

large a field can be planted if the yield has been at the rate of 
200 bushels per acre? 

Fourth and Subsequent Years. — Continue this same scheme, 
constantly discarding the poor units and selecting the best for 
breeding. 

Estimate how large your breeding plot should be in order to 
supply a 5-acre field with seed in the third year, supposing the 
yield from your selected units to be the same as the average 
yield given by the 25 best selected units in your former report^ 
i.e. about 370 bu. per acre. 

Scheme for Corn Breeding Plots 

All corn breeding and increase plots should be at least 1200 
feet from any other corn. Why? 

First Year. — Select from the field 100 ears. From these 
choose the best 50 for planting a breeding plot the next year. 

Second Year. — From these 50 ears, plant a breeding plot 
by the ear-to-row method. Rows should be 4 feet apart, hills 
3 feet apart in the row, each row to contain 100 hills. Surround 
the breeding plot with 2 or more border rows planted with seed 
from the unused select ears. Why? Detassel alternate halves 
of adjacent rows. Why? Select from the best 10 or 12 rows 
50 to 100 of the best ears, choosing the best 50 for the next 
year's breeding plot. Save the seed from the other best-yielding 
rows for an increase plot, or the general field. 

Third Year. — ■ Plant your breeding plot as before, with the 
best selected 50 ears. With the other selected ears plant an 
increase plot or general field. Select as before the best 50 ears 
from the breeding plot for the next year's breeding plot, saving 
the remainder for a new increase plot. Save ears from this 
year's increase plot for planting next year's field. 

Fourth and Subsequent Years. — As before, plant your breed- 
ing plot, increase plot, and field, using a continuous and pro- 
gressive scheme of selection. 



Appendix E 467 

Scheme for Wheat Breeding Plots 

First Year. — Choose 100 fine heads for starting your improve- 
ment work. 

Second Year. — • Plant seed from these select plants in short 
rows b^' the plant-to-row method. Space the rows 1 foot apart. 
Select a few rows, say twenty, to furnish seed for a breeding plot 
in the third year. 

Third Year. — Plant seed from each of these select rows in a 
breeding plot. Do not mix the seed from different rows. Plant 
as many 17 foot rows in each plot as the amount of seed saved 
will permit. This is at the rate of 1| bushels per acre. The 
rows should be 1 foot apart. 

Fourth Year. — Find average yield of progeny rows that came 
from the selected rows of the third year. Select several of the 
best strains which may yield about 24 bu. per acre. With this 
seed plant increase plots from each kind of seed. Save seed from 
2 or 3 of the best jdelding plots for more extensive trials in the 
5th year. The rest of the seed can be used for planting a field. 
Make new selections of heads in the fields and repeat the whole 
program as before. There may be many more valuable types 
in the fields that can thus be isolated. 

Fifth Year. — Test out your select strains and choose one or 
two of the best for increase plots and for planting your field. 
Plant the field this year with seed from last year's increase plot 
and from the test rows. 

Scheme for Oat or Barley Breeding Plots 

The principles of selection and methods of breeding these 
cereals are the same as for wheat. 



INDEX 



Absence factors, 192. 

Acquired characters, 17. 

Adami, M., 145. 

Adams fund, 314. 

Adam's laburnum, 142. 

Adaptation, 7, 37, 106. 

Alfalfa, 313. 

Alkali resistance, 313. 

Allelomorph, 325. 

Allen, Dr., 314, 315. 

American Seed Trade Association, 
309. 

Anemone coronaria, 57, 58. 

Animals, breeding, 217. 

Anthers, 276. 

Anthocyanin, 186. 

Antirrhinum {see snapdragon). 

Apples, 212, 255, 295 ; hybrid, 235. 

Arthur, 228, 239. 

Artificial selection, 37. 

Asexual propagation and hybridi- 
zation, 125. 

Asparagus, 313. 

Associations, plant-breeding, 300. 

Atavism, 211, 231. 

Average deviation, 47. 

Barker, E. E., 394. 

Bartel, T. C, 254. 

Barteldes, 264. 

Bateson, 155, 183, 187, 192. 

Beans, 260 ; Emerson's experiments 

with, 189. 
Bibliography, 335. 
Biometry, 41, 325. 
Biotypes, conception of, 19. 
Blackberries, hybrid, 136. 



Blackberry, 253. 

Books, plant-breeding, 328. 

Braun, Alexander, 20. 

"Breaking the type," 22, 219. 

Breeding periodicals, 332. 

Breeding plants, rules for, 222. 

Broughton, Mr., 91. 

Browne, Dr. Thomas, 56. 

Bruant, 237. 

Brunella vulgaris, 80. 

Brussels sprouts, 243. 

Budd, Professor, 258. 

Buds, methods of emasculation, 
291. 

Bud-selection, 39, 242. 

Bud-sports, 210, 241. 

Bud-variation, 11, 29. 

Bud-varieties, 242. 

Burbank, 112, 321. 

Burpee, 264. 

Burr, "Field and Garden Vege- 
tables," 295. 

Cabbage, evolution of, 267 ; savoy, 
244 ; shapes, 245 ; wild, 240. 

Camerarius, 110. 

Canadian Seed Growers' Associa- 
tion, 304. 

Cannas, 237, 265. 

Capsella Heegeri, 80. 

Car ex, little natural crossing in, 
103. 

Carnation, 179. 

Carri^re, 58, 223, 239, 296. 

Castle, 180. 

Cauliflower, 248. 

Cavalier, wheat, origin of, 91. 



469 



470 



Index 



Cereals, disease-resistant, 313. 

Change, of seed, 28 ; of stock, results 
from, 105, 107. 

Chelidonium, 55, 56. 

Cherries, hybrid, 235. 

Chimaera, 146, 148. 

Chromoplasts, 186. 

Chromosome, 325. 

Chrysanthemum, 251, 252, 253, 
256, 257, 258, 259, 262, 263, 264, 
267, 268, 269; carinatmn, 226; 
indicum., 250 ; inodorum plenis- 
simum, 87 ; morifolium, 249 ; sege- 
tum, 86, 89 ; segetum plenum, 86, 
88. 

Citranges, 132, 312. 

Citrus trifoliata, 312. 

Climate, as factor in variation. 25, 
26 ; man's control over, 27. 

Coefficient of heredity, 152 ; of va- 
riability, 49. 

Collard, 242. 

Color, mendelian inheritance of, 185. 

Commercial breeding agencies, 308. 

Compositae, 223. 

Compositous flowers, 279. 

Corn breeding, 216. 

Correns, 155. 

Cotton, 213, 214, 312, 313. 

Council of grain exchanges, 310. 

County agent, the, 310. 

Cowpeas, disease resistance, 220. 

Cross, function of, 101, 230. 

Crosses, characteristics of, 123. 

Crossing, a means not an end, 232 ; 
and change of seed, 103 ; effects 
on the species, 97 ; from stand- 
point of plant improvement, 108 ; 
how to overcome antipathy to, 
121; limits of, 97. 98, 99; process 
of, 281 ; refusal result of natural 
selection, 100 ; vigor as result of, 
112, 115. 

Crossing animals, 216. 

Crossing plants, philosophy of, 92. 

Crozy, 237. 



Cucumber pollinations, 141. 
Cultivation, philosophy of, 24. 
Cupid sweet pea, 77. 
Curled kale, 241. 
Cytisus Adami, 142, 145. 

Darwin, 20, 34, 52, 59, 73, 105, 107, 

111, 113, 209, 240, 242, 244, 296, 

307. 
Dates, 313. 

Davenport, C. B., 183. 
Davenport, E., 149. 
Davis, Bradley Moore, 318. 
Deviation, average, 47 ; standard, 48. 
de Vries, Hugo, 52, 53, 59, 62, 63, 

72, 73, 74, 76, 79, 155. 
Dewberry, 253. 
Dihybridism, 171. 
Dioecious flowers, 278. 
Disease resistance, 219, 220, 313. 
Dominance, 165 ; incomplete, 179. 
Dominant characters, 325. 
Dorsey, M. J., 424. 
Double flowers, experiments in 

production of, 86 ; history of 

appearance of, 56. 
Downing' s "Fruits and Fruit 

Trees," 295. 
Draba, 73. 

Drought-resistant plants, 313. 
Duggar, B. M., 318. 
Duplex, 325. 
Durum wheat, 313. 

Ear-to-row, 308. 
East, E. M., 318. 
Eckford, 237. 
Egg-plant, 128, 141. 
Egyptian cotton, 313. 
Elderberry, 217, 218. 
Elementary species, 63, 80. 
Emasculation, 282. 
Emerson, 189. 

Environment as a cause of varia- 
tion, 16, 216. 
Epistatic, 325. 



Index 



471 



Error, probable, 50. 
Evening-primrose {see (Enotbera). 
Evening-primroses, laws of muta- 
bility of, 72. 

Factor hypothesis, 326. 

Fairchild, Thomas, 110. 

Fertilization, 270. 

Flowers, structure of, 270. 

Fluctuating variations and muta- 
tions, 54. 

Focke, 232. 

Food supply, as cause of variation, 
20, 21 ; of different branches, 23. 

Frequency curve, 42. 

Fultz wheat, origin of, 91. 

Galton curve, 326. 
Gametes, 168, 326. 
Garden varieties, origin of, 18. 
V Gartner, C. F., 110, 111. 
Genetics, 326. 
Genotype, 326. 

Germ-plasm, action of environ- 
ment upon, 17. 
Gibb, 258. 

Gideon, Peter M., 233. 
. Gladiolus, 237. 
Glossary, 325. 
Gmelin, J. G., 110. 
Goff, 228, 229. 

Gold Coin wheat, origin of, 91. 
Gourds, 140. 
Graft-hybrids, 142. 
Grain exchanges, council, 310. 
Grapes, 212, 235 ; hybrid, 133. 
Gray, Asa, 35. 
Green, Ira W., 91. 

Hallock & Son, 247. 
Harper, R. A., 318. 
Head-to-row, 308. 
Helianthemum, 73. 
Henderson, 264. 

Heredity, 149; coefficient of, 152.; 
studied collectively, 149. 



Heterozygote, 326. 

History of mutation, 55. 

Homozygote, 326. 

Hopetown wheat, origin of, 91. 

Hurst, 192. 

Husk-tomato pollination, 141. 

Hybridization and asexual prop- 
agation, 125. 

Hybridized, what plants can be, 
111. 

Hybrids, 326 ; history of, 1 10 ; defini- 
tion of, 108 ; influence of sex on, 
138 ; production of, 101 ; vari- 
ability of, 122. 

Hyper-chimsera, 148. 

Hypostatic, 326. 

Ideal, 220. 

Illinois Seed Corn Breeders' Associa- 
tion, 303. 

Immature seeds, 228. 

Implements of pollination, 292. 

Improvement of plants, systematic, 
295. 

In-breeding, 127. 

Indeterminate varieties, 209. 

Individuality, fact of, 2. 

Individual selection, 308. 

Inhibitor, 180. 

Inter-crossing, swamping effects of, 
98. 

Ipomoeas, 229. 

Kinshu rice, 313. 

Knight, Thomas Andrew, 110. 

Kohl-rabi, 248. 

Kolreuter, J. G., 110. 

Kumerle, J. W., 265. 

Laboratory exercises, 394. 

Lamar k, 59. 

Lemoine, 237. 

Lettuce, improvement in, 221. 

Linaria vulgaris {see toad-flax). 

Linaria vulgaris peloria, 84. 

Linnaeus, 110, 138. 



472 



Index 



Locke, 180. 
Lupines, 231. 

Maize, 224. 

Mass selection, 307. 

Mean, 45; use of, 46. 

Measurement of, 41. 

Mendel, 155. 

Mendelian inheritance of color, 185. 

Mendelian ratio, 179. 

Mendelism, application to plant- 
breeding, 202, 225 ; in wheat, 194 ; 
limits of, in the production of 
new varieties, 204 ; of tomatoes, 
203 ; summarized, 200. 

Mendel's experiments, 156. 

Mendel's law, explanation of, 158. 

Methodical selection, 307. 

Minnesota Field Crop Growers' As- 
sociation, 303. 

Mirdbilis, 112. 

Modal coefficient, 45. 

Mode, 44. 

Monoecious flowers, 277. 

Monotypic genera, 224. 

Moore, Jacob, 235. 

Morning-glories, Darwin's experi- 
ments with, 114. 

Morse & Company, 77. 

Morus multicaulis, 299. 

Munson, Professor, 117, 235. 

Munting, Abraham, 57. 

Mutability, laws of, with evening- 
primroses, 72. 

Mutants, how produced in the 
garden, 71. 

Mutation, history of, 55 ; first use 
of word, 56. 

Mutations, 40, 52, 326 ; economic 
significance of, 90 ; and fluctua- 
tions, 54 ; can they be produced 
artificially ? 200 ; examples of, 76 ; 
experimental study of origin of, 
84 ; frequency of occurrence of, 79 ; 
mutations resulting from men- 
delian segregation and recombi- 



nation, 193 ; mutations which 
mendelize are constant, 193. 

Natal and post-natal variations, 18. 

Natural hybrids, rarity of, 102. 

Natural selection, 34, 93 ; as cause 
of variation, 14. 

Navel oranges, 313. 

Nectarines, 241. 

New York Plant Breeders' Associa- 
tion, 304. 

Nicotiana pollinations, 142. 

Nilsson, Professor, 304. 

Nulliplex, 326. 

Oats, Swedish select, 313. 

(Encthera albida, 63, 67, 71, 74 
analytical table of seedlings 
68-69 ; brevistylis, 63, 64, 71, 74 
de Vries' experiments with, 59 
elliptica, 64, 68, 71, 74; gigas 

63, 65, 66, 71, 74; loevifolia, 63 

64, 71, 74 ; Lamarkiana, 59, 60 
61, 64, 71, 74; lata, 64, 67, 71 
74 ; muricata, 60 ; nanella, 60 
63, 64, 71, 74; oblonga, 63, 67 
71, 74 ; rubrinervis, 63, 65, 71 
74; scintillans, 64, 68, 71, 74 
variations in stature of, 53. 

Ohio Plant Breeders' Association, 

304. 
Olives, drought-resistant, 313. 
Ononis repens, 80. 
Organs, essential, 274. 
Orton, 313. 

Palmer, Asa, 264. 

Peaches, 212. 

Peas, Mendel's experiments with, 

157. 
Pedigree culture, 308. 
Pelargoniums, 237. 
Peloric toad-flax, 79. 
Pepino pollination, 141. 
Pepper pollinations, 141. 
Peppers, 222. 



Index 



473 



Perennial plants, 241. 

Periclinal chimaera, 148. 

Periodicals, breeding, 332. 

Phenotype, 327. 

Physalis, 104. 

Pineapple hybrids, variation of, 123. 

Pistils, 271. 

Plant-breeding : associations, state, 
300; books, 328; by selection, 
218; defined, 212; forward 
movement in, 294 ; instruction, 
321 ; laboratory, U. S. Dept. 
Agri., 311; projects, 315; use 
of term, 296. 

Plant improvement a serious busi- 
ness, 298. 

Plant introductions, division of, 
312. 

Plants, differences compared with 
animals, 10. 

Plant-to-row, 308. 

Plateation, 397 ; defined, 327. 

Plums, 212, 294. 

Pollen, 280. 

Pollen storage, 289. 

Pollination, 270 ; process of cross, 
281, 289; uncertainties of, 140. 

Poncirus trifoliata, 312. 

Population, 41. 

Potatoes, 241. 

Presence-and-absence hypothesis, 
181. 

Pride Butte wheat, origin of, 91. 

Probabilities, theorem of, 169. 

Probable error, 50. 

Punnett, 183, 184. 

Quetelet curve, 44. 

Radishes, division of, 239. 
Raspberries, hybrid, 235. 
Recessive characters, 327. 
Recessiveness, 165. 
Regel, cited, 295. 

Reproduction, difference between 
plants and animals, 10. 



Retrograde varieties, 65. 
Rogers' grape hybrids, 235. 
Roguing, 251. 
Russian apples, 212, 258, 295. 

Savoy cabbage, 244. 

Score card, use of, 236. 

Sea Island cotton, 312. 

Sectional chimaera, 148. 

Seed, change of, 28. 

Segregation, 327. 

Selection, accumulative, 209 ; ar- 
tificial, 37, 243 ; individual, 308 ; 
mass, 307 ; methodical, 307 ; 
plant-breeding by, 218. 

Sex, a factor in variation, 15, 215; 
influence on hybrids, 138 ; origin 
and function of, 95. 

Shirley poppy, 76. 

Shull, 190, 318.- 

Simplex, 327. 

Snapdragon, 83. 

Snyder blackberry, 255. 

Solanaceous plants, 222. 

Solarium darwinianum, 147; Gdrt- 
nerianum, 147 ; graft-hybrids, 146 ; 
kolreuterianum, 147 ; proteus, 147 ; 
tubingense, 146. 

Somatic, 327. 

Species, definition, 8. 

Species-formation, 8. 

Spencer, 105. 

Spillman, 180, 194. 

Sport, 39. 

Sprenger, 55. 

Squares, method of, 169. 

Squashes, 128, 140. 

Stamens, 271. 

State experiment stations, 310. 

State plant-breeding associations, 
302. 

Statistical methods (see biometry). 

St. Hilaire, Geoffroy, 58. 

Stout, A. B., 318. 

Struggle for life, a cause of varia- 
tion, 30. 



474 



Index 



Sturtevant, 228. 

Sugar beets, variation in amount 

of sugar in, 54. 
Swede turnip, 248. 
Swedish Seed Association, 304. 
Swedish select oats, 313. 
Swingle, Walter, 312. 
Systematic improvements of plants, 

295. 

Tangelo, 133, 312. 
Teas' Weeping mulberry, 233. 
Teosinte, 137. 
Thomson, 149. 
Thymus vulgaris, 80. 
Timothy, variability of, 3. 
Toad-flax, 79, 81, 82. 
Tobacco pollinations, 142. 
Tomato, 215, 222, 228, 244, 246; 
ignotum, 246; pollinations, 141. 
Trihybrid, 177. 
Tschermak, 155, 188. 
Tuber-unit, 308. 
Type, 43. 

Unit-characters, 9, 154. 
United States Dept. Agri., 310. 
Uses, breeding for specific, 224. 

Variability, biometrical expression 
of, 43, 47; coefficient of, 49. 

Variation, action of natural selec- 
tion upon, 14 ; and adaptation, 7 ; 
causes of, 13, 30, 94 ; caused by 
environment ; caused by sex 
differences, 15 ; in climate, 25 ; 
choice and fixation of, 34 : de 
Vries' classification, 53 ; fluctuat- 
ing, 54 ; in food supply, 20 ; 



measurement of, 41 ; natal and 
post-natal, 18. 

Varieties, "coming true," 210, 211 ; 
how they originate, 209 ; inde- 
terminate, 209 ; non-uniformity 
of, 19 ; outright production of, 
by crossing, 118 ; retrograde, 63 ; 
spontaneous appearance in wild 
state, 79. 

Variety, what is it ? 35. 

Verlot, 244, 296. 

Vigor as result of crossing. 112, 115. 

Vilmorin, 226, 230, 231, 269. 

Vitis, 122. 

Vries, de, Hugo (.sec de Vries). 

Walker, Ernest, 243. 
Wallace, 105, 123. 
Watermelons, wilt-resistant, 219. 
Wealthy apple, 233. 
Webber, 133, 156, 312. 
Weismann, 16, 17. 
Wheat, Durum, 313. 
Wheatland fife wheat, origin of, 91. 
Wheat-rye hybrid, 136. 
Wier, D. B., 233. 
Wild cabbage, 240. 
Wilks, Rev. W., 76. 
Willis, 117. 

Wilson, strawberry, 248. 
Wilt-resistant watermelons, 219. 
Winkler, Professor, 146, 148. 
Wisconsin Agricultural Improve- 
ment Association, 300. 

Xanthein, 187. 
Xenia, 327. 

Zygote, 327. 



The following pages 

contain advertisements of books by the same 

author or on kindred subjects 



CYCLOPEDIA OF 
AMERICAN AGRICULTURE 

Edited by L. H. BAILEY 

With 100 full-page plates and more than 2,000 illustrations in the 
text; four volumes; the set, $20.00 net; half morocco, $32.00 net. 



Vol. I — Farms Vol. Ill — Animals 

Vol. II— Crops Vol. IV— The Farm and the Community 



This is unquestionably the most important agricultural cyclopedic 
work published in this country. The leading experts in the United 
States and Canada, both investigators and practical farmers, con- 
tribute to its chapters, which are arranged not alphabetically, but 
topically, each subject being treated in its various aspects by men 
especially familiar with it. It contains advice for the city man who 
is seeking a home in the country, as well as for the professional 
farmer. The book is strictly new and up-to-date in its methods and 
advice, thoroughly readable, and a standard work of reference. It 
is profusely illustrated, about one-third of the total space being 
assigned to illustrations — all original. 

"Indispensable to pubhc and reference libraries . . . readily 
comprehensible to any person of average education." — The Nation. 

"The completest existing thesaurus of up-to-date facts and 
opinions on modern agricultural methods. It is safe to say that many 
years must pass before it can be surpassed in comprehensiveness, 
accuracy, practical value, and mechanical excellence. It ought to 
be in every Ubrary in the country." — Record-Herald, Chicago. 



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'''■The Bible and Britannica of the Garden-folk'' — The Nation 

The Standard 
Cyclopedia of Horticulture 

Edited by L. H. BAILEY 

With the assistance of over 500 collaborators 

New edition, entirely rewritten and enlarged with many features, with 24 plates 

in color, 96 full-page half-tones and over 4,000 text illustrations. 

To be complete in six volumes. 

Each volume: Cloth, $6.00; Leather $10.00. 
Sold only in sets by subscription. 



Two opinions of Volume I of the new Cyclopedia: 

"No one who knows anything at all about the hterature of garden- 
ing needs to be told that the Cyclopedia is unique. It is the Bible 
and Britannica of the garden-folk, amateur and professional alike. 
And the remarkable thing is that, while it is fundamentaly a work 
of reference, it also contains limitless quantities of good reading of 
the sort dear to the heart of the garden enthusiast." — The Nation. 

"It is no exaggeration to state that Bailey's new work is the best 
cyclopedia obtainable for all who are connected, either remotely or 
intimately, as amateurs or professionals, with horticultural pursuits. 
It is the best for the student of botany who is investigating the subject 
in a purely scientific way; best for the commercial grower who Ukes 
to be well informed on matters in general and his own trade in par- 
ticular, and best for the other sort of commercial grower, who does 
not bother himseK particularly about hunting for any information 
except such as will give him immediate help in producing a better 
crop." — The Florist's Review. 



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f 



THE RURAL MANUALS 

Edited by L. H. BAILEY 
MANUAL OF FRUIT INSECTS 

By MARK VERNON SLINGERLAND and 
CYRUS R. CROSBY 

Of the New York State College of Agriculture, at Cornell University 

Illustrated, 12mo, 503 pages, $2.00 net; postage extra. 

A MANUAL OF WEEDS 

By ADA E. GEORGIA 

Assistant in the Farm Course, New York State College of Agriculture, 

Cornell University 

With 385 Illustrations by F. SCHUYLER MATHEWS 

Illustrated, cloth, Vlmo, 593 pages, index, S2.00 net: postage extra. 

MANUAL OF FARM ANIMALS 

A Practical Guide to the Choosing, Breeding and Keep of 
Horses, Cattle, Sheep and Swine 

By MERRITT W. HARPER 

Assistant Professor of Animal Husbandry in the New York State 
College of Agriculture, at Cornell University 

Illustrated, V2mo, 545 pages, index, $2.00 net; postage extra. 
"A book deserving of close study as well as being handy for lefeience, 
and should be in the possession of every farmer interested in stock." — ■ 
Rural World. 

MANUAL OF GARDENING 

A Practical Guide to the Making of Home Grounds and the 
Growing of Flowers, Fruits and Vegetables for Home Use 
By L. H. BAILEY 

Illustrated, cloth, 12mo, 544 pages, $2.00 net; postage extra. 

This new work is a combination and revision of the main parts of 

two other books by the same author, "Garden-Making" and "Practical 

Garden Book," together with much new material and the result of the 

experience of ten added years. 

THE FARM AND GARDEN RULE BOOK 

By L. H. BAILEY 

Revised and enlarged edition — Illustrated, cloth, 12mo, $2.00 net. 

It is essentially a small cyclopedia of ready rules and references 

packed full from cover to cover of condensed, meaty information and 

precepts on almost every leading subject connected with country life. 



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The Rural Outlook Set 

By L. H. BAILEY 

Four Volumes. Each, cloth, 12ino. Uniform binding, attractively boxed, 
$5.00 net per set; carriage extra. Each volume also sold separately. 

In this set are included three of Professor Bailey's most popular books 
as well as a hitherto unpublished one, — "The Country-Life Movement." 
The long and persistent demand for a uniform edition of these little 
classics is answered with the publication of this attractive series. 

The Country Life Movement 

Cloth, 12mo, 220 pages, $1.25 net; postage extra 

This hitherto unpublished volume deals with the present movement 
for the redirection of rural civilization, discussing the real country-life 
problem as distinguished from the city problem, known as the back-to-the- 
land movement. 

The Outlook to Nature (New and Revised Edition) 

Cloth, l2mo, 195 pages, $1.25 net; postage extra 

In this alive and bracing book, full of suggestions and encouragement, 
Professor Bailey argues the importance of contact with nature, a sympa- 
thetic attitude toward which "means greater efficiency, hopefulness, 
and repose." 

The State and the Farmer (New Edition) 

Cloth, 12mo, $1.25 net; postage extra 
It is the relation of the farmer to the government that Professor 
Bailey here discusses in its varying aspects. He deals specifically with 
the change in agricultural methods, in the shifting of the geographical 
centers of farming in the United States, and in the growth of agricultural 
institutions. 

The Nature Study Idea (New Edition) 

Cloth, 12mo, $1.25 net; j^ostage extra 
"It would be well," the critic of The Tribune Farmer once wrote, "if 
'The Nature Study Idea' were in the hands of every person who favors 
nature study in the public schools, of every one who is opposed to it, and 
most important, of every one who teaches it or thinks he does." It has 
been Professor Bailey's purpose to interpret the new school movement 
to put the young into relation and sympathy with nature, — a purpose 
which he has admirably accomplished. 



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RURAL TEXT- BOOK SERIES 

Edited by L. H. BAILEY 
Each volume illustrated. Cloth, 12mo. 



While the RURAL SCIENCE SERIES is designed primarily for 
popular reading and for general use, this related new series is designed 
for classroom work and for special use in consultation and reference. 
The RURAL TEXT-BOOK SERIES is planned to cover eventually 
the entire range of pubUc school and college texts. 

DUGGAR, B. M. 

Physiology of Plant Production $1 bU net 

DuGGAR, John Frederick 

Southern Field Crops I 7iy net 

Gay, C. Warren i -r^ * 

Principles and Practice of Judging Live-Stock . 1 ^0 net 

Harper, M. W. ^ ^ -, ^r^ , 

Animal Husbandry for Schools 1 ^0 net 

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Grasses i c>V net 

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Field Crop Production I 4i) net 

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Principles of Soil Management 1 7d net 

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Beginnings in Agriculture io net 

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Elements of Agriculture i lu net 

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